The ability of six proposed chemopreventive agents to prevent diethylnitrosamine-induced liver foci and tumors in male C3H mice was investigated. The test agents were administered by intraperitoneal injection on days 13, 14 and 15 of age and starting at 21 days of age continuously in the diet until sacrifice at 161 days of age. The mice were administered 4.0 mg/kg diethylnitrosamine by intraperitoneal injection on day 15 of age and two hours after the test agent. Diethylnitrosamine-induced 62.4 +/- 4.2 foci of altered hepatocytes and 22.1 +/- 2.1 hepatocellular adenomas, which were reduced by diallyl sulfide to 21.6 +/- 2.4 and 6.73 +/- 1.13 and phenethyl isothiocyanate to 28.2 +/- 3.4 and 5.06 +/- 1.53 foci and adenomas, respectively. Difluoromethylornithine and ellagic acid only decreased the yield of adenomas without affecting the yield of foci of altered hepatocytes and of total lesions. N-Acetyl-l-cysteine and 1,2-oxothiazolidine-4-carboxylate did not affect the yield of either liver lesion. When administered starting prior to diethylnitrosamine-initiation and continuing until sacrifice, diallyl sulfide and phenethyl isothiocyanate demonstrated chemoprevention of tumorigenesis.