Acute organophosphate intoxication in man is well known to result in substantial central nervous system dysfunction. To test the hypothesis that similar neurobehavioral abnormalities might be present in mild degree in workers chronically exposed to organophosphate pesticides, 23 such subjects were tested for abnormalities in memory, signal processing, vigilance, language, and proprioceptive feedback performance. The performance of the exposed workers was not deficient in any of the five measures assessed when compared with the performance of a control group matched for age and educational background. Plasma and red blood cell cholinesterase levels were found to be in the normal range in both exposed and control groups, although plasma levels of exposed subjects were depressed somewhat below control values. Relative resistance of higher nervous system functions to mild chronic organophosphate exposure is suggested by these results.