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.