We report a 60-yr-old woman with schizophrenia, who manifested a neuroleptic malignant (NM)-like syndrome after acute organophosphate poisoning (OPP). She attempted suicide by ingesting 40% emulsions of DMTP (S-2,3-dihydro-5-methoxy-2-oxo-1,3,4-thiadizol-3-yl-methyl O,O-dimethyl phosphorodithioate) 100 ml. On admission, she was unconscious and demonstrated convulsions, depressed respiratory movements, miosis and profuse salivation. Plasma cholinesterase concentration (842 IU.L-1) was very low and OPP was diagnosed. She was treated with gastric lavage, atropine and pralidoxime (PAM). By the seventh day after admission, symptoms of OPP disappeared and serum ChE had recovered to a sub-normal level. On the 13th day, she demonstrated coma, high fever (41.0 degrees C) and lead-pipe rigidity. Serum CPK was increased (1631 IU.L-1). Dantrolene sodium iv was administered for three days. Body temperature began to decrease in 24 hr, and her consciousness, muscle rigidity and other neurological symptoms returned to normal by the 16th day after admission. She was discharged from the hospital without sequelae 55 days after admission. We conclude that OPP can predispose to an NM-like syndrome and that dantrolene may be effective in the management.