Lead nitrate and acetate are potent liver mitogens in the Wistar rat. Prior exposure to these agents has been found to alter their susceptibility to hepatotoxins. The present study assessed the capacity of both lead compounds to cause mitogenicity in the liver of adult male and female rainbow trout. Groups treated with a single intravenous or intraperitoneal injection of lead nitrate or lead acetate exhibited no statistically significant (P < 0.05) alterations in liver/body weight ratio nor hepatic DNA content. Results provide evidence of significant interspecies variation in the mitogenic response of rainbow trout and Wistar rats to the mitogenic potential of lead in the liver.