Dibutylhexamethylenediamine (CAS No. 4835-11-4) was evaluated for acute inhalation toxicity in 6 male Charles River rats exposed to dynamically-generated vapors at analytical concentrations of 0.12, 0.21, 0.22, 0.27, 1.38, and 3.64 mg/L for 4 hours. Vapors produced by a syringe-fed Lindberg tube furnace (190-220 degrees C) were carried by 4-5% N2/minute into a 20 L battery jar exposure chamber, which was also oxygen supplemented to approximately 20% by infusion of houseline air. Samples of chamber air in acetone were analyzed for vapor concentrations by gas chromatograph fitted with a flame ionization detector. A LC50 was 0.22 mg/L (95% confidence limits, 0.13 - 0.28 mg/L). Most rats died during exposure, although one rat of the 0.27 mg/L exposure group died four days post-exposure. Clinical signs of toxicity characterizing all exposures included pawing and chewing, salivation, lethargy, and irregular breathing. Exposure levels of 0.21 mg/L and higher were associated with convulsions, which were most severe at the highest exposure levels. Nasal discharge (sometimes red) was noted among rats of the high level exposure, while hyperemia was documented at all other exposure levels. Red or clear nasal and ocular discharge, irregular respiration, gasping and lung noise, and transient weight loss were observed among survivors at all exposure levels during the 14-day post-exposure recovery period. A Haskell Laboratory system of toxicity classification determined that 98% 1,6-hexanediamine, N,N-dibutyl- is highly toxic by inhalation.