Injections of 2.5 mg/kg of stellate sturgeon (Acipenser stellatusPall.) pituitary extract and 5 mg/kg of carp (Cyprinus carpioL.) pituitary extract in Siberian sturgeon (Acipenser baeriBrandt) females did not reveal significant differences in the effects of these preparations. There were no differences in the percentage of females that responded by ovulation, duration of the period from injection to ovulation, rate of ovulation, or quality of mature eggs as estimated by the percentage of fertilization or percentage of normal embryos at the small yolk plug stage. Thus, an insufficient efficiency in the artificial reproduction of the Siberian sturgeon grown in captivity is not related to the use of the carp pituitary preparation as a stimulus. Estimation of the ratio of specific activities of the pituitary extracts and purified gonadotropins of the stellate sturgeon and carp by in vitrooocyte maturation has shown that it varies within wide limits as a function of the medium composition and physiological state of follicles. Hence, the ratio of activities of the gonadotropins of different species as determined by in vitromaturation of sturgeon oocytes may markedly differ from that upon injection of these preparations in breeders.