Previous studies have demonstrated that dietary administration of the schistosomicidal drug 5-(2-pyrazinyl)-4-methyl-1,2-dithiole-3-thione (oltipraz) ameliorates the hepatotoxicity of aflatoxin B1 (AFB1). Notably, mortality, altered hepatic function, hepatic AFB1-DNA adduct levels, and expression of hepatic enzyme-altered foci were markedly reduced in the rat by concurrent feeding of oltipraz during exposures to AFB1. Collectively, these studies prompted us to evaluate the chemoprotective properties of oltipraz against AFB1-induced liver cancer. In addition, preliminary molecular dosimetry studies were undertaken to determine the utility of measurements of urinary aflatoxin-N7-guanine excretion as a marker of relative risk for hepatocarcinogenesis in AFB1-exposed rats. For the carcinogenesis studies, 5-wk-old male F344 rats were randomly divided into two groups. One group (55 rats) received the AIN-76A diet, and the other group (56 rats) received the AIN-76A diet supplemented with 0.075% oltipraz. The oltipraz-supplemented diet was fed for 4 wk. Beginning 1 wk after starting the experimental diets, all rats in both groups received 25 micrograms of AFB1/rat/day by gavage for 5 days per wk over the next 2 wk. One wk following cessation of dosing with AFB1, oltipraz was removed from the diet, and all rats were fed the AIN-76A diet for the remainder of the experiment. At 3 mo after dosing, livers of ten sentinel rats from each group were analyzed for the burden of gamma-glutamyltranspeptidase-positive foci. In accord with previous findings, rats fed the oltipraz-supplemented diet exhibited substantial reductions in the focal burden (97% reduction; P less than 0.05) of these AFB1-induced lesions. The remaining rats were maintained for the cancer study until they became moribund or the termination of the experiment at 23 mo. Gross liver lesions were identified at autopsy and confirmed by microscopic evaluation. An 11% incidence of hepatocellular carcinoma was observed in the AFB1-treated, control diet-fed rats. An additional 9% of this group had hepatocellular adenomas. Oltipraz afforded complete protection against both AFB1-induced hepatocellular neoplasms. Using Kaplan-Meier survival analyses, rats in the oltipraz group had a significantly (P less than 0.02) longer life span and an increased survival free of liver tumors (P less than 0.0002). Molecular dosimetry studies used rats fed either the oltipraz-supplemented or control diet for 1 wk and then challenged with a single dose of AFB1 to examine the initial rates of 8,9-dihydro-8-(N7-guanyl)-9-hydroxyaflatoxin B1 excreted in the urine.(ABSTRACT TRUNCATED AT 400 WORDS)