Effects of allyl chloride on occupationally exposed subjects were studied in two factories manufacturing sodium allyl sulfonate. Twenty-six subjects in factory A and 27 workers in factory B were exposed to allyl chloride at levels of 2.6-6 650 mg/m3 for 2.5 months--6 years and 0.2-25.13 mg/m3 for 1-4.5 years, respectively. Most subjects of factory A had weakness, paresthesia, and numbness in extremities with sensory impairment in the glove-stocking distribution, as well as reduced ankle reflexes. Electroneuromyography showed neurogenic abnormalities in 10 of the 19 subjects examined, the prevalence of neuropathy therefore being 52.6%. Similar symptoms of workers in factory B were clinically much milder, and there were few abnormal neurological signs--yet electromyographic findings indicating mild neuropathy were found in 13 of the 27 subjects. No significant abnormalities of other organs were noted. Possible etiologic factors other than exposure to allyl chloride were excluded. All the evidence obtained indicates that chronic exposure to allyl chloride mainly causes toxic polyneuropathy. The neurotoxicity of allyl chloride has also been confirmed by experimental neuropathological studies.