Neuromuscular (NM) changes resulting from organophosphate exposure are known to be complex. After severe acute poisoning recovery from initial depolarisation paralysis may be followed in a limited number of cases by onset of a non-depolarisation paralysis (the Intermediate Syndrome). It is not clear whether this block arises subclinically in all cases of poisoning as a sequel to the initial depolarisation. 2. Single fibre electromyography (SFEMG) is a sensitive clinical neurophysiological technique allowing detection of subclinical changes at the neuromuscular junction. In the study reported it has been used to examine changes in NM transmission in the forearm of fit volunteers exposed to a low level of sarin (isopropyl methyl phosphonofluoridate). 3. Small changes in SFEMG were seen at three hours and three days after an exposure sufficient to cause a reduction in red cell acetyl cholinesterase to 60% of normal. The SFEMG changes were not accompanied by any clinical neuromuscular symptoms or signs and returned to normal 2 years after exposure. 4. The results indicate that there are reversible subclinical changes compatible with the development of non-depolarising NM block without frank clinical expression. In the small population examined there were individual variations in response which may reflect differences in safety margin at the neuromuscular junction.
