Subchronic inhalation toxicity was evaluated in groups of 10 male Crl:CD BR rats exposed to formamide vapors at analytical concentrations of 0, 113, 500 and 1504 ppm for 6 hours/day, 5 days/week for 2 weeks. Mortality was observed in 2 rats in the 1504 ppm exposure group. Clinical observations included diarrhea, red nasal and ocular discharges, and hunched posture. Statistically significant (p < 0.05) decreases in body weights were observed in all animals in the highest exposure group. Hematological examination revealed statistically significantly (p < 0.05): decreased MCV values, platelet counts and lymphocytes in animals in the highest exposure group; increased MCHC values and decreased platelet counts in animals exposed to 500 ppm; and increased atypical lymphocytes in animals in the lowest exposure group. Clinical biochemistry findings included a statistically significant (p < 0.05) decreases in: thrombocytopenia in males at 500 and 1504 ppm; lymphopenia in animals exposed to 1504 ppm; and increases in serum cholesterol in animals exposed to 1504 ppm. There were no exposure-related urinalysis findings. Microscopic histopathological examination revealed nephrosis characterized by degeneration and necrosis of the tubular epithelium, minimal to severe renal lesions, and mineralized necrotic debris surrounded by granulomatous inflammation in male rats exposed to 1504 ppm; all other findings were condidered to be unrelated to the test material. Increased relative kidney weights were observed in animals exposed to 1504 ppm. Gross necropsy findings were not reported.