Research was performed on the effect of tea, or tea and milk, instead of drinking water, in rat models of cancer in the mammary gland or colon. Solutions of 1.25% (w/v) black tea, or 1.85% (v/v) milk in tea were prepared three times per week. SD rats were given tea beginning at 42 days of age; one group was gavaged 5 mg 7,12-dimethylbenz[a]anthracene (DMBA) at 49 days of age; another group received 8.4 mg 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) twice per week beginning at age 49, then 14 mg twice a week for 4 weeks more. The groups on DMBA were killed 33 weeks later, and those on IQ 39 weeks later. Tea decreased the mammary gland tumor multiplicity and volume, and milk and tea had a greater protective action. Male F344 rats were given two doses of 15 mg/kg azoxymethane (AOM) on weeks 6 and 7, and some groups started on tea, or tea and milk at 5 weeks; one group started on tea 2 days after AOM. Foci of aberrant crypts in the colon were decreased, after 9 weeks, in the groups on tea, or tea and milk during AOM administration, but not after AOM. Thus, tea decreases mammary tumor induction, and the production of foci of aberrant crypts in the colon. Milk potentiates these inhibiting effects.