The acute oral toxicity of isomeric-monobutylamines was investigated in Sprague-Dawley-rats. Male and female rats were administered 100, 200, 300, 400, 500 or 600 milligrams per kilogram (mg/kg) body weight of n-butylamine (109739), isobutylamine (78819), and sec- butylamine (13952846) and doses of 30, 40, 50, 70, 100 or 200 mg/kg tert-butylamine (75649) by gavage. Animals were observed for toxic reactions or mortality for 14 days. At death, animals were subjected to gross pathologic examination. Signs of toxicity observed included sedation, ataxia, nasal discharge, gasping and salivation, followed by convulsions and death at high doses. Pulmonary edema was noted on gross pathological examination. Tert- butylamine was the most toxic followed by sec-butylamine and isobutylamine with n-butylamine being the least toxic. The authors conclude there was a four fold difference in lethal dose for 50 percent of animals between the most and least toxic compounds tested, and there were no sex related differences in the toxicity of the monobutylamines.