The effectiveness of pyridostigmine pretreatment against soman poisoning has been determined in rhesus monkeys and marmosets receiving atropine therapy. Pretreatment with the maximum sign‐free dose (200 μg kg−1, i.v.) raised the subcutaneous LD50 of soman by a factor of 28 in rhesus monkeys and 15 in marmosets. Theprotection afforded by a quarter of the sign‐free dose of pyridostigmine was not significantly less. These levels of protection are higher than any reported in non‐primate species.