Using various anti-carcinogenic agents (nitrogen mustard N-oxyd as an alkylating agent, 8-azaguanine as an anti-metabolite, and sarcomycin-Na, carzinophilin, mitomycin C, chromycin, actinomycin and sanamycin as inhibitory anti-carcinogenic agents) the authors studied the actions of these agents on the spermatozoa and eggs of sea-urchin by observing the rates of the membrane formation at insemination and egg division and obtaind the following results. 1. When treated with the solution of various anti carcinogenic agents diluted ten-fold the optimal qunatity for the human body for ten minutes, the spermatozoa of sea-urchin (Heliocidaris crassistina) are hardly affected by these agents. 2. In the cases where sea-urchin eggs (Hemicentrotus Pulcherrimus) are treated for 30 minutes with different anti-carcinogenic agents at various concentrations, the higher the concentration, the greater is the decrease in the rates of the membrane formation and egg division at insemination of normal spermatozoa, and in the case treated with the solution diluted 50-fold of the optimal quantity for the human body the inhibitory action of the agents increases in the ascending order of: carzinophilin > Thio TEPA > N itrogen mustard > mytomycin > Sanamycin > chromomycin > actinomycin. 3. When treated with the 50-fold solution these agents as compared with the proximal concentration for the human body, at the intervals of 20, 40, 60. 80, and 90 minutes after the fertilization, mytomycin and carzinophilin markedly inhibit the fusion of male and female nuclei while chromomycin, sarcomycin and nitrogen mustard suppress the cell division at metaphase, and chromomycin has especially strong inhibitory action on the cell. 4. When the effects of these agents are compared with those of OX-substance with respect to their concentration, it has been clarified that the action of these agents on sea-urchin eggs and spermatozoa are weaker than that of OX substance.