To test the hypothesis that chronic neurologic sequelae are associated with cholinesterase depression short of frank organophosphate poisoning, we compared 45 male subjects who had a history of moderate cholinesterase inhibition with 90 male subjects who had neither past cholinesterase inhibition nor current pesticide exposure. Cholinesterase-inhibited subjects were defined as having had a history of (a) red blood cell cholinesterase at 70% or less of baseline or (b) plasma cholinesterase at 60% or less of baseline absent symptoms of frank poisoning. In the subject comparison evaluation, only 1 of 27 neurologic tests (i.e., serial digit performance) was significant statistically, but it was opposite of the direction hypothesized. In a companion study for which the same battery of neurologic tests and the same subjects were used, neurologic sequelae were related to high exposures among subjects who sought treatment for organophosphate poisoning. The data in the current study, in which the subjects experienced lower exposures short of frank poisoning, provide some evidence that preventing acute organophosphate poisoning also prevents neurologic sequelae.