Early treatment of organophosphate (OP) poisoning with oximes results in reactivation of acetylcholinesterase and patient recovery. Data on efficacy of late administration of oximes, particularly obidoxime, is limited. A 42-y old woman swallowed 60 ml of 50% malathion in a suicide attempt. Characteristic muscarinic, nicotinic and central manifestations of OP poisoning appeared: atropine and 250 mg obidoxime i.v., resulted in marked improvement. Several hours after the last dose, clinical manifestations recurred and ventilation was required. After 10 d cholinesterase was still low and liver enzymes were elevated. Obidoxime was reinstituted after the 9 d interruption and muscle strength improved with the first dose. The patient could be disconnected from the ventilator and within <24 h was extubated. Oxime therapy should be considered even late in the course of untreated or partially treated OP intoxications, especially when the etiologic agent is a lipid-soluble compound (ie malathion) that can cause a protracted course of poisoning. The clinical course of this patient did not support a cause-and-effect relationship between obidoxime and the abnormal liver function.