The effects of lethal (2.0 mg/kg) and high sublethal (1.3 mg/kg) dosages of the organophosphate acetylcholinesterase (AChE) inhibitor paraoxon on FR10 performance rate was determined 1 and 2 days after intoxication. The lethal doses were antidoted with either centrally acting atropine sulfate (AS), or atropine methyl bromide (AMB) or atropine methyl nitrate (AMN), both quaternary salts and not expected to act centrally. AChE inhibition in the brain was about 35-60% on the second day after treatment. AS yielded a small transient depression in performance, while AMB and AMN yielded severe deficits, with incomplete recovery. Performance was depressed by 1.3 mg/kg paraoxon by 52% and 34% on days 1 and 2, respectively, while performance was more greatly depressed by the lethal dose, especially with the noncentrally acting antidotes: AS, 67 and 48%; AMB, 81 and 55%; AMN, 91 and 78%. However, a low dose of AS with 2 mg/kg paraoxon resulted in very severe, nonrecovering deficits. A lethal dose of the nonpersistent anti-AChE eserine sulfate, antidoted with a low dose of AS, yielded no deficits. Thus, a high level, acute intoxication with paraoxon yields behavioral deficits which are attenuated by high levels of a centrally acting muscarinic receptor antagonist. The paraoxon-induced performance deficits or their recovery do not correlate directly with AChE inhibition.