This study aimed to investigate whether occupational exposure to organophosphate (OP) pesticides caused neurophysiological abnormalities. Thirty farmers who regularly spray OP pesticides and 30 fishermen (controls), living close by but not involved in pesticide spraying, were evaluated during and between cultivation seasons. The farmers had higher erythrocyte acetylcholinesterase levels than the controls during (P = 0.06) and between cultivation seasons (P = 0.09). During the cultivation season, there was a significant reduction in erythrocyte acetylcholinesterase activity in both groups (P < 0.01). Significant differences between the farmers and controls were found in sensory conduction velocity (P = 0.04) and motor conduction velocity (P = 0.04) between cultivation seasons. Sensory conduction velocity was reduced significantly in farmers (P < 0.01) and in controls (P = 0.04) during the cultivation season. Effects of OP poisoning were seen both in farmers and in controls, who had no history of spray activities. Evidence of sensory dysfunction after acute exposure and sensory and motor impairment after long-term low-level exposure to OP was seen.