Nonhuman primates which were fed Mestinon (pyridostigmine) syrup-impregnated food biscuits (40 mg per animal) exhibited a reproducible inhibition of whole blood cholinestrase activity of 40 to 50% for a period of 1 to 6 hr. Pyridostigmine pretreatment was supplemented by therapy with two doses of an antidotal combination (A,TM,B) consisting of 0.05 mg/kg atropine, 2.24 mg/kg TMB-4, and 0.4 mg/kg benactyzine which assured survival in five of six animals following three separate exposures to 10 LD50 soman. The protective period of this oral dose of pyridostigmine supported by A,TM,B therapy was between 1/2 and 8 hr. Oral pyridostigmine pretreatment in combination with atropine therapy (three doses of 0.07 or 1.00 mg/kg im) also saved monkeys exposed to 10 LD50 soman; however, the period of recovery was prolonged. Oral pyridostigmine pretreatment did not alter the lethality of soman in the absence of A,TM,B or atropine therapy.