To study the effect of chronic alcohol consumption on tumor development due to dimethylnitrosamine (DMN) administration, female Sprague-Dawley rats were pair-fed for 3 weeks a nutritionally adequate liquid diet containing either ethanol (36% of total calories) or isocalorically substituted carbohydrates as control diet. Thereafter, the animals were maintained on laboratory chow and tap water ad libitum for another 2 weeks and received 1.5 mg DMN i.p. per day for the first 5 days. This 5-week cycle was repeated three more times. Chronic treatment with an alcohol-containing diet was shown to significantly improve the mean survival time of DMN-treated rats compared with identically treated animals fed the control diet, but the total number of tumors observed under these experimental conditions and the target organ remained virtually unchanged.