Corroborated here is the fact, earlier established by Chulitskaya and Felgengauer (1977), that the cytoplasm of mature non-activated eggs of Rana temporaria and Acipenser stellatus, unlike that of Rana pipiens, exerts no cytostatic effect on the nuclei of the cleaving embryo, but acquires such a capacity after being treated with EGTA. EGTA treatment imparts cytostatic properties also to the cytoplasm of cleaving embryos. Revealed is the dependence of the cytostatic effect and death of injected embryos on the dose of EGTA introduced into the egg. No mitotic figures have been detected in embryos with a cytostatic effect. Upon reciprocal transplantation of the cytoplasm between Rana temporaria and Xenopus laevis, only the latter's cytoplasm possessed a cytostatic effect, while the arrest at a metaphase was found only in a few arrested blastomeres.