Reserpine, chlorpromazine, perphenazine, meprobamate, nidroxyzone and Enheptin (2-amino-5-nitrothiazole), drugs previously shown to inhibit estrus in intact mice, were studied for their effects on subestrus occurring after ovariectomy in C3H mice. None of these drugs, administered by the drug-diet method, had any effect on either the frequency of subestrus smears after their establishment or the development of subestrus. Other findings in ovariectomized mice were: (1) the frequency of subestrus smears tended to decrease with time and (2) restriction of food intake in mice with well established subestrus did not alter the frequency of subestrus smears.