Male swiss mice were implanted with Ehrlich ascites tumor cells and fed ad libitum either yogurt or yogurt components. Ad libitum feeding of yogurt for 7 consecutive days after tumor implantation significantly (P<0.05) inhibited cell counts by 24 to 28% and DNA synthesis by 23 to 31%. When milk or 1.5% lactic acid was fed, there was no significant effect. Feeding yogurt for 7 d before implantation, in addition to yogurt feeding for 7 d after implantation, did not increase inhibition. The level of inhibition was decreased, however, when feeding was initiated more than 1 d after tumor implantation. While yogurt effectively inhibited initial tumor growth, continuous feeding from day 1 until death had no significant effect on the survival rate of the mice. Centrifugal separation of yogurt into solids and supernatant fluid fractions revealed that the antitumor activity was localized in the solids fraction; the supernatant fluid possessed no activity. Concentration of the solids fraction did not significantly i...