the organophosphorous anticholinesterase agents diisopropylfluorophosphate (dfp) and soman were applied topically, by way of cotton pledgets placed bilaterally to three different chemosensitive areas of the ventral medulla of the cat, and the effects on cardiorespiratory activity were monitored. the dose range was 6.25-25.0 microgram/side dfp and 0.004-0.5 micrograms/side soman comparison of dose-response data upon application to the three areas indicated that both agents exerted their greatest effect at the intermediate area. oxotremorine, a specific agonist for muscarinic receptors, also had a much greater effect on cardiorespiratory activity when applied to the intermediate area as compared to its effects after application to either the caudal or the rostral areas further evidence indicating the role of a muscarinic receptor in mediating the respiratory depressant effects of dfp and soman at the intermediate area was the finding that atropine counteracted the toxic effects of these compounds. the intermediate area was also found to be rich in cholinesterase activity