The degree and duration of the hypoglycemic effect of monocomponent insulin (MC-A) using different doses were examined in comparison with conventional insulin (C-A) using normal rabbits and rabbits immunized with beef insulin. There were no significant differences between MC-A and C-A for the maximal rate and the duration of the hypoglycemic effect with the three doses (0.25U/kg, 0.5U/kg, and 1.0U/kg) in both animal groups. However maximal hypoglycemic responses to 0.5U/kg of MC-A and to 0.5 U/kg of C-A in normal rabbits were almost the same as that of MC-A 1.0U/kg and of C-A 1.0 U/kg and these responses were one and a half times as strong as MC-A 0.25U/kg and C-A 0.25 U/kg, although the duration of the effect almost responded in proportion to the doses. On the other hand, in immunized rabbits, there was no significant difference among the maximal hypoglycemic rate with each three doses. On the contrary, the duration of the insulin effect was delayed with the three doses and especially, the duration of the insulin 0.25U/kg effect continued the same as insulin 0.5U/kg after 4 periods. Also, the duration of the insulin 1.0U/kg the effect was significantly delayed as compared with the previous two doses and was not recovered to pre-injection level even at the 8th period.