The peripheral blood lymphocyte chromosome was examined after 2.5h

in a case of

60

Co exposure accident. The frequency of dicentric plus ring was 89%

thus radiation dose of 4.78 (4.53—4.88) Gy was estimated. The examinations of lymphocyte chromosome aberration within following 6 years showed that the incidence of dicentric plus ring decreased quickly and fluctuated at low level after the 3rd year post exposure

while the number of cells with stable aberrations remained practically unchanged and showing a tendency to increase. It is suggested that for estimative dose after exposure the Dic+R predominant

but in case of studying the late effect the stable aberrations was indispensable.