The antidotal action of atropine with trimedoxime, obidoxime or methoxime against isopropyl methylphosphonofluoridate intoxication in mice was studied. The best antidotal effect was demonstrated for the combination of atropine and methoxime (tested as therapeutic index or D50 index). The effect of atropine (constant dose) and methoxime (different doses) on acetylcholinesterase (AChE) activity in four parts of the mouse brain following isopropyl methylphosphonofluoridate intoxication was described. The therapeutic effect could be improved by increasing dose of methoxime. AChE activity in the pontomedullar area was increased on increasing the dose of methoxime (p less than 0.005). A correlation between residual AChE activity in the pontomedullar part of the mouse brain and mortality was demonstrated.