Table of Contents Preface. I. Dose Estimation. High background radiation area - an important source of exploring the health effects of low dose ionizing radiation (L.-X. Wei). Exposures to natural radiation worldwide (B.G. Bennett). Cosmic ray contribution in the measurement of environmental gamma ray dose (K. Nagaoka, K. Honda, K. Miyano). Survey of natural radiation background and assessment of its population dose in China (K.-D. Wei et al). Investigation of outdoor &ggr;-radiation level in Suzhou urban and rural areas (Y. Tu, D.-Z. Jiang). Environment ionizing radiation level and dose to population in Qinghai province (Z.-Y. Cao et al). Methodology of external radiation dosimetry and measurement assurance applied in epidemiology in high background radiation area in Yangjiang, China (K.-B. Li, S.-A. Zhao). II. Radioactive Aerosols. World high level natural radiation and/or radon-prone areas with special regard to dwellings (M. Sohrabi). Origin of a new high level natural radiation area in the hot spring region on Mahalat, central Iran (M. Sohrabi et al.). Level of 222Rn and its daughters in the environment of Xinglong district in Hainan Province (Q.-X. Zeng et al.). Radon concentration and radiation dose to the population exposed in the high elevation areas of Sichuan (Y.-G. Liu, Y.-H. Mao). 222Rn concentration in different types of cave dwellings in Gansu Province (P.-Y. Gao et al.). Concentration of radon and its daughters in environment and internal doses to population in Qinghai Province (J.-Q. Ni et al.). The size distribution of atmospheric radioactive aerosols and its measurement (Y.-H. Jin et al.). A newsub-nationwide survey of outdoor and indoor 222Rn concentrations in China (Y.-H. Jin et al.). III. Natural Radionuclides. Indian research on high levels of natural radiation: pertinent observations for further studies (P.C. Kesavan). Brazilian research in areas of high natural radioactivity (A.R. Oliveira et al.). Natural radioactivity of soil samples in some high level natural radiation areas of Iran (M. Sohrabi et al). Investigations about the radioactive disequilibrium among the main radionuclides of the thorium decay chain in foodstuffs (D.C. Lauria et al.). Transfer of 226Ra, 228Ra, 210Po in the aquatic organism and the foodstuff chain (X.-T. Yang et al.). Intake of food and internal doses by ingestion in two high radiation areas in China (H.-D. Zhu). Biosphere effects of natural radionuclides released from coal-fired power plants (Y.-H. Mao, Y.-G. Liu). IV. Fallout from Nuclear Test. Overview of scope-RADTREST project (R. Kirchmann et al.). Assessment of risks from combined exposures to radiation and other agents at environmental levels (T. Jung, W. Burkart). Exposure dose from natural radiation and other sources to the population in China (C.-S. Zhu, Y. Liu, L.-A. Zhang). Transfer of nuclear fission products to crops and soils and countermeasures (S.-M. Xu et al.). Dosimetry study of residents near Semipalatinsk nuclear test site (J. Takada et al.). Radioactive contamination in North Xinjiang resulting from former USSR atmospheric nuclear tests in 1962 (J.-L. Hou et al.). Observations in Kyoto, Japan of radioactive fallout from Chinese atmospheric nuclear explosion tests (N. Fujinami). Epidemiological Study. Methodology of epidemiology in low dose radiation exposure (H. Kato). Recent advances in dosimetry investigation in the high background radiation area in Yangjiang, China (Y.-L. Yuan et al.). Study of the indirect method of personal dose assessment for the inhabitants in HBRA of China (H. Morishima et al.). Databases and statistical methods of cohort studies (1979-90) in Yangjiang (Q.-F. Sun et al.). Study on cancer mortality among the residents in high background radiation area of Yangjiang, China (Z.-F. Tao et al.). Infant leukemia mortality among the residents in high-background radiation areas in Guangdong, China (S. Akiba et al.). Confounding factors in radiation epidemiology and their comparability between the high background radiation areas and control areas in Guangdong, China (Y.-R. Zha et al.). Epidemiologic study of cancer in the high background radiation area in Kerala (M. Krishnan Nair et al.). Radiation associated lung cancer in northern Iran (R.M. Raie, Z. Taherzadeh Boroujeny). A survey of senile dementia in the high background radiation areas in Yangjiang, Guangdong Province, China (J. Li et al.). Advanced cytogenetical techniques necessary for the study of low dose exposures (I. Hayata). Preliminary report on quantitative study of chromosome aberrations following life time exposure by high background radiation in China (T. Jiang et al.). Effect of low dose rates on the production of chromosome aberration under lifetime exposure to high background radiation (S. Nakai et al.). Cytogenetic findings in inhabitants of different ages in high background radiation areas of Yangjiang, China (D.-Q. Chen et al.). Cytogenetic studies in lymphocytes of healthy inhabitants of Mazandaran a high level of natural radiation area in Iran (R.M. Raie, M. Aledavoud). VI. Radiation Hormesis. The radiation paradigm regarding health risk from exposures to low- ose radiation (T. Sugahara). Cellular and molecular basis of the stimulatory effect of low dose radiation on immunity (S.-Z. Liu). A survey of long-term and low dose radiation effect on SIL-2R in residents (Z.-Y. Zeng et al.). Immune competence and immune response to virus in high background radiation area, Yangjiang, China (J.-M. Zou et al.). Stimulatory effect of in vivo exposure to enriched uranium oxyfluoride on DNA excision repair in mouse lymphocytes (Z.-S. Yang, S.-P. Zhu, S.-Q. Yang). VII. Adaptive Response and Genetic Effects. Adaptive response in human beings living in the area contaminated by Chernobyl accident (I. Pelevina et al.). Investigation on the adaptive response to ionizing radiation induced by high background exposure to spa workers (S.-Y. Yao et al.). Techniques for detecting the genetic effects of the atomic bombings applicable to the study of the genetic effects of natural radiation (C. Satoh et al.). Genetic instability induced by low-dose radiation (M. Watanabe et al.). Experimental study of the genetic effects of high levels of natural radiation in South-France (M. Delpoux et al.). VIII. Summary and General Discussion. IX. Concluding Remarks. X. Start of International Committee on High Levels of Natural Radiation and Radon Areas. XI. Appendix.