N,N,N',N'-Tetramethyl- 1,6-Hexanediamine (TMHD), Sample No. 8361-12, was evaluated in male and female Fischer 344 rats for acute oral toxicity. The test material was administered by gavage at dose levels ranging from0.1 to 1.0 mL/kg. One group of animals from each sex was dosed with distilled water and served as controls. TMHD caused 100% lethality in both sexes at dose levels of 0.5 and 1.0 mL/kg. No females died at a dose of 0.1 at/kg while 2 of 5 males (40%) died at this dose level. The oral LOSO for this material in the rat should be considered to be between 0.25 and 0.5 mL/kg for females and 0.1 and 0.5 mL/kg for males. TMHD caused significant depressions in absolute body weight and body weight gains in both sexes. A generalized depression in neuromuscular function occurred following exposure with peripheral, central and autonomic functions being affected. A number of clinical observations and necropsy findings suggested that TMHD was markedly damaging to the gastrointestinal system, particularly the stomach and surrounding organs. Microscopic examination revealed necrosis of the gastrointestinal tract, localized peritonitis and necrosis of the liver and pancreas. Additional lesions were identified in the lung, liver, kidneys, thymus, lymph nodes and spleen which were directly or indirectly related to exposure to TMHD. A no-effect level was not established in this study.