Groups of young adult male Fischer-344 rats given the vehicle (corn oil) or either decalin or d-limonene at dose levels of 75, 150 or 300 mg/kg body weight by a single daily gavage on 5 days/wk were killed on study days 6 or 27, approximately 24 hr after the fifth or 20th dose, to determine whether the specific time- and dose-related triad of renal alterations characterizing decalin-associated nephrotoxicity in the adult male rat also occurs in response to d-limonene. Dose-related hyaline droplet formation associated with renal accumulation of a specific protein alpha 2u-globulin) is considered the primary response in the morphogenesis of decalin-induced nephrotoxicity in the male rat and was present to a maximal degree in all decalin- and d-limonene-treated groups by day 6. Alterations considered to be sequelae of the hyaline droplet response, including granular casts in the outer zone of the medulla and multiple cortical changes collectively classified as chronic nephrosis, were present in the kidneys of both decalin- and d-limonene-treated rats killed on day 27. These findings demonstrate a uniformity of primary and secondary renal responses to the two chemicals, strongly suggesting that the morphogenesis of d-limonene-associated nephrotoxicity in the adult male rat is consistent with that of decalin. The response of the male rat kidney to decalin treatment has been shown to be uniquely different, by virtue of anatomical, physiological and biochemical peculiarities involving the proximal convoluted tubule, from that in female rats and higher mammalian species.