Organophosphate-induced hypothermia in rodents appears to be due to stimulation of muscarinic receptors in the anterior hypothalamus. The nerve agent soman (pinacolyl methylphosphonofluoridate) produced a transient hypothermia in mice. Concomitant with the recovery from soman-induced hypothermia, which was complete within 6 hr, there was a parallel recovery of the hypothalamic acetylcholinesterase activity. Pretreatment of mice with the protein synthesis inhibitor, cycloheximide, did not affect the recovery from soman-induced hypothermia nor the recovery of hypothalamic acetylcholinesterase activity. The results suggest that the recovery from soman-induced hypothermia may be due to the recovery of acetylcholinesterase, perhaps from the assembly of previously synthesized precursors.