Acute inhalation toxicity was evaluated in groups of 6 male Crl:CDBR rats exposed to formamide at mean analytical concentrations of 1.3, 2.0, 5.1, 14, 19 or 21 mg/L for 4 hours. The test atmosphere was generated by metering the test material into a round-bottom flask heated to 100-210 deg C for concentrations less than 19 mg/L. The two highest atmospheric concentrations were generated with a nebulizer. Mortality was observed in 1 animal in the 21 mg/L dose group; the ALC was reported to be 21 mg/L. Clinical observations included lethargy, hunched posture, ocular and nasal discharges, partially-closed eyes, diarrhea, brown-stained perineum, and weight loss. Gross necropsy was not reported.