Electrophysiological studies in suicidal patients with organophosphate poisoning are reported. Patients often developed muscular weakness of variable severity owing to diplorisation block at nicotinic receptors. During such paralysis nerve conduction velocity and distal latencies were normal even in severely paralysed patients. The amplitude of the compound action potential was smaller than in controls and often showed a repetitive response. The amplitude tended to be lower in those more severely affected. On repetitive stimulation there was usually no decrement with three stimuli per second and only occasional decrement at 10 per second. At 30 Hz several cases showed a decrement even in the absence of paralysis. This response to repetitive stimuli is thus quite distinct from that seen in either myasthenia or Eaton Lambert syndrome. On three occasions after poisoning with dichlorovos there was first anticholinesterase insecticide poisoning and later delayed neurotoxicity as seen with triorthocresylphosphate. These cases showed all the features of a severe pure motor axonal degeneration neuropathy.