Background The effects of exposure to chemical warfare agents in humans are topical. Porton Down, near Salisbury, is the UK’s centre for research on chemical warfare. Since WWI, a programme of experiments involving approximately 30 000 participants drawn from the UK armed services has been undertaken there.

Objectives Our aim is to report on exposures to nerve agents, particularly sarin, using detailed exposure data in a cohort of servicemen who attended Porton Down.

Methods We have used existing data on exposures to UK servicemen who attended the human volunteer programme at Porton Down to examine exposures to nerve agents in general and to sarin in particular.

Results Six principal nerve agents were tested on humans, all between 1945 and 1987. Of the 4299 nerve agent tests recorded, 3511 (82%) were with sarin, most commonly in an exposure chamber, with inhalation being the commonest exposure route (85%). Biological response to sarin exposure was expressed as percentage change in cholinesterase activity and, less commonly, change in pupil size. For inhalation tests, assessed by changes in red blood cell cholinesterase median inhibition for was 41% (IQR 24%–51%), with a maximum of 87%. For dermal exposures, assessed by changes in unspecified cholinesterase, median inhibition was 22% (IQR 10%–37%), with a maximum inhibition of 99%. There was a clear association between increasing exposure to sarin and depression of cholinesterase activity but the strength f the association varied by exposure route and the presence of chemical or physical protection. Pupil size decreased with increased exposure but this relationship was less apparent when protection was present.

Conclusions These results, drawn from high quality experimental data, offer a unique insight into the effects of these chemical agents on humans.

Acknowledgement We thank Nicola Fear and Gemma Archer, our collaborators in new work on these data, for their input.