A subchronic 90-day inhalation study was conducted to determine the toxic effects of decalin, a commonly used industrial solvent. Experimental groups consisting of male and female beagle dogs, male and female Fischer-344 rats, and female C57BL/6 mice were continuously exposed to decalin concentrations of 5 or 50 ppm. An unexposed control group was also maintained. All dogs and a portion of each rodent group were sacrificed and examined at exposure termination, while the remaining rodents were held for observation up to 21 months postexposure. No distinct exposure-related lesions were noted in dogs. Dog body weights, organ weights, and blood clinical pathology were also normal. At exposure termination hepatocellular cytoplasmic vacuolization was noted in female mice exposed to both concentrations. This liver tissue change was reversible and was not a significant finding in female mice examined during the 21-month postexposure observation period. In male rats, decalin exposure produced nephropathy characterized by hyaline droplets, necrosis, and intratubular casts. Accentuated tubular degeneration and medullary mineralization were noted in exposed rats held for long-term postexposure observation. There was no associated abnormal increase in mortality nor alterations in serum, blood urea nitrogen, or creatinine levels. Female rats were free of decalin-induced renal damage. There was a slightly greater incidence of commonly occurring pituitary tumors in both mice and rats; however, the tumor incidence was not dose related. The results of this study suggest that the toxic effects of decalin are similar to those previously described for other hydrocarbon solvents and fuels.