Past research (Diamond and Young, 1963) has shown that progesterone is capable of inhibiting male-like sexual behavior from being induced in a female guinea pig by testosterone propionate (T.P.). This present study was designed to investigate the possibility of inhibiting normal male sexual behavior.

Four groups of normal male guinea pigs were given weekly tests of sexual behavior for 3 consecutive 10 week periods. The first period served to establish a base line of behavior for all groups. Following the 19th weekly test the first group of males remained intact and the second group was castrated. For control purposes both groups received daily injections of sesami oil. The third group received daily I.M. injections of progesterone and the fourth group was castrated and given simultaneous injections of T.P. and progesterone.

During the third 10 week period the two groups of castrated animals were injected with T.P. and the intact animals were untreated.

The results indicate that progesterone is capable of inhibiting normal male sexual behavior regardless if the male is castrated or not. This inhibition is temporary and normal behavior returns after cessation of the progesterone treatment. A suggestion was seen that the hormonal regimen may be more effective than castration in suppressing sexual behavior.

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