Normal dog blood lymphocytes were irradiated by

60

Co

γ

-rays at doses of 0.50

0.25

0.05

0.01 and 0.005 Gy with dose-rates of 0.20

0.10

0.01

0.003

0.001 and 0.0003 Gy per min. in vitro. Lymphocyte survival was distinguished with an exclusion test of trypan blue. The results from the examination at intervals of 0.4 and 8h after exposure suggest that a relation between effects and doses is not obvious at the initial duration and is gradually increased with time by a linear correlation. On the other hand

an inverse dose rate effects on lymphocyte survival was observed from begining to end.