EN
Balantidium coli grown on Pawłowa's medium at pH 6.8, temperatur of 37° was adapted for 72 days to increasing concentrations of penicillin (0.001-60 mM) It was found that penicillin at the concentrations of 0.01-1.0 potentiates the division frequency of the protozoon; in 10 mM penicillin solution the number of adapted individuals does not differ from that of control. Balantidium coli adapted to 20 mM penicillin solution was examined for the sensitivity to 300 mM piperazine, 100 mM histidine and 8 mM atebrine solution. After 20 minutes the mortality of penicillin adapted protozoa in these solutions was 55.68 and 0%, respectively, in contrast to control ones which died in 100%/ p > 99%.