It is well known that the effect of organophosphate pesticides on the autonomic nervous system is a cholinergic reaction. However no study has been done assessing the effect of organochlorine pesticides on the autonomic nervous system. We evaluated the autonomic nerve function using open-loop pupillography in 20 patients who had exposure to the organochlorine pesticides. Significant differences were seen in pupil area (p less than .006), velocity of both constriction and dilatation (p less than .001), and dilatation time (p less than .02), when compared with 18 normal subjects. Autonomic nerve disturbances were detected in eighteen of 20 patients (90%) by evaluating the pupillary light reflex in each patient. Sympathetic nerve inhibition i.e. sympatholytic pattern, was recognized in ten of 18 patients (55%). Four patients with sympatholytic pattern had a disturbance not only in the sympathetic nerve, but also parasympathetic nerve involvement suggesting pandysautonomia. The residue blood level of the organochlorine pesticides was examined in each patient. A high frequency of the DDE was recognized (85%). It was concluded that the toxicity of the organochlorine pesticide on the autonomic nerve appear as an inhibitory effect on pupil light reflex.