The carcinogenicity of sodium benzoate was examined in Fischer 344 rats. Sodium benzoate was administered in the diet for 18 to 24 months at two dose levels; concentrations of 2% and 1% in the diet, which corresponded to the maximum tolerated dose (MTD) and 1/2 MTD as estimated from the data obtained by 6-week toxicity study. Fifty males and 52 females each were used per group. Controls consisted of 25 male rats and 43 female rats. No adverse clinical signs directly attributable to the compound were observed in treated animals. Differences in the average body weight, and mortality rates between treated and control groups were negligible. The results of the statistical test for dose-related trends were not significant (p < 0.05) Although a variety of tumors occurred among test and control rats of each sex, tumors appearing in treated rats were similar in type and number to those in controls. It was concluded that no evidence of carcinogenicity in rats from sodium benzoate was demonstrated.