Over the past decade there have been significant developments in the techniques and methods of monitoring radon and radon daughters, thoron and thoron daughters, and radioactive dusts encountered in the mining and milling of radioactive ores. The development of new techniques and methods of measurement has received increased attention owing to the fact that the efficient control of radon and its daughters in the mining atmosphere, particularly in underground mines, is a difficult task. Epidemiological studies have clearly demonstrated that the incidence of lung cancers among underground uranium miners, and also among underground non-uranium miners who were exposed to radon and radon daughters in their occupations, is higher than that among the general public. This publication is a revision of IAEA Safety Series No. 43, originally issued in 1976. The revised version has been limited in coverage to radiation monitoring and medical surveillance.