Peroxisome proliferators are a class of compounds which induce hepatomegaly and peroxisome proliferation in liver parenchymal cells. One of the earliest known effects of peroxisome proliferators is the rapid transcriptional activation of the genes responsible for the peroxisomal beta-oxidation system in liver. Long term administration of these chemicals to rats and mice results in the development of hepatocellular carcinomas. Here we report that mRNA for alpha 2u-globulin, a rodent male specific protein, is markedly reduced or undetectable by Northern blot analysis of total RNA in the livers of rats treated with ciprofibrate. This was further confirmed by immunoblot analysis using antibodies against alpha 2u-globulin. Nevertheless, immunohistochemical staining and in situ hybridization showed respectively the presence of a few cells that contained alpha 2u-globulin protein and its mRNA. The alpha 2u-globulin mRNA reappeared in the liver 2 weeks following the cessation of ciprofibrate treatment. Feeding of ciprofibrate for two weeks followed by simultaneous feeding of ciprofibrate and a nephrotoxic chemical d-limonene for 5 weeks revealed that ciprofibrate prevented the renal accumulation of alpha 2u-globulin and the nephrotoxicity associated with the binding of d-limonene with alpha 2u-globulin.