The effects of orotic acid consumption on hepatic lipid and nucleotide metabolism were examined concurrently in the rat. When orotic acid was fed at 1.0%, fatty liver development was evident by day 7 but not by day 3, whereas a decreased purine/pyrimidine ratio of hepatic acid-soluble nucleotides was noted by day 3. As nucleotide changes preceded hepatic fat accumulation, they could be a contributing factor in the etiology of fatty liver. When fed for 10 days, rats did not accumulate hepatic fat on a diet containing 0.1%, but did on 0.5 and 1.0%; similarly, the purine/pyrimidine ratio was not significantly affected on 0.1% but was decreased on both 0.5 and 1.0% orotic acid. These results indicate that orotic acid alters both hepatic lipid and nucleotides when consumed by rats at a level above 0.1%. As measured in these studies, hepatomegaly did not always accompany hepatic steatosis and appeared to be a subsequent development. In addition, L-dihydroorotate was shown to be as effective as orotic acid in increasing hepatic weight and lipid whereas uridine was ineffective.