To evaluate chronic effects of acute organophosphate pesticide poisoning, quantitatively determined vibrotactile thresholds were measured as an index of peripheral neuropathy among agricultural workers in Nicaragua. Thirty-six male workers were evaluated between 10 and 34 months after hospitalization for acute organophosphate poisoning and compared to an age- and sex-matched community reference group. Vibrotactile thresholds were measured quantitatively in right and left index fingers and right and left great toes. Study subjects were stratified into three groups: 1) never poisoned; 2) poisoned with organophosphates other than methamidophos, agents which have not been reported to cause peripheral neuropathy; and 3) poisoned with methamidophos, a peripheral neurotoxin. For all digits, there was a statistically significant trend of increasing age- and height-adjusted thresholds across these three exposure categories. Over one fourth of patients previously poisoned with methamidophos we studied had abnormal vibrotactile thresholds. These results suggest that previously reported cases of organophosphate-induced delayed polyneuropathy may represent only the worst disease in a spectrum of impairment, a sequela of exposure that may be much more common than previously thought.