The LC50 of nitrogen trichloride (NCl3) was determined in rats following a one hour inhalation exposure. Five groups of 10 animals per group were exposed to a concentration range of NCl3 from 58 ppm to 157 ppm. The one hour LC50 is 112 ppm with the 95% confidence interval between 107 ppm and 117 ppm. All mortality occurred during or within one day following the exposure. Gross necropsy of the animals which died as a result of exposure to NCl3 showed noticeable fluid in the trachea and lungs. This was not the case for those animals which survived the exposure (gross necropsies performed 14 days post-exposure). Pulmonary edema appears to contribute significantly to mortality produced by NCl3.