In a three-generation reproduction study, rats were given caprolactam in the diet of 0, 1000, 5000 and 10,000 ppm. No treatment-related effects were observed in the parental animals with respect to mortality, clinical signs, reproductive performance or gross pathology findings. Consistently lower body weights were noted in the P2 and P3 mid- and high-dose males and females. Consistently lower mean food consumption values were noted in the P2 and P3 mid- and high-dose males and the high-dose females. These differences were generally significant (P less than or equal to 0.05) in the high-dose group of both sexes. Compound-related histopathologic findings noted in the high-dose P1 males consisted of a slight increase in the severity of spontaneous nephropathies, occasionally accompanied by granular casts. The offspring data revealed no treatment-related effect with respect to gross appearance, gross pathology, survival, number of pups, percentage of male pups or kidney weight. Analysis of the offspring body weights on Days 1, 7 and 21 of lactation revealed consistently and generally significant lower mean values in the high-dose male and female animals of all filial generations. The mean body weights of both sexes in the mid-dose group were generally lower than those of the controls. The effects on mean body weight, mean food consumption and the group increases in the severity of nephropathy, accompanied by the presence of granular casts in some animals, are considered to be related to the administration of caprolactam.