[en] Peripheral blood lymphocytes from unirradiated control subjects and workers exposed within permitted limits to γ-radiation, have been examined for the incidence of dicentric and acentric chromosome aberrations. The results are compared with a review of data published elsewhere. Background levels show inter-laboratory variation and possible reasons for this are discussed. By combining the present data with those from the literature the spontaneous incidence of dicentric aberrations is approx. 0.55 x 10^-3 and for acentrics is 3.7 x 10^-3. In occupationally exposed subjects a significantly higher incidence of aberrations was found. When allowance was made for the turnover of lymphocytes for the period over which each man had worked with radiation a linear dose-effect relationship was apparent. The incidence of dicentrics was 2.22 +- 0.94 x 10^-4 rad^-1 and for all unstable aberrations 8.24 +- 2.8 x 10^-4 rad^-1. These are in reasonable agreement with dose-response data obtained in vitro. (orig.)