In male Sprague-Dawley rats, motor and sensory conduction velocities (MNCV and SNCV) of the tail nerve decreased significantly as a result of oral administration of 400 and 200 mg/kg of 2,5 hexanedione (2,5-HD) once daily, 5 days a week for up to 7 and 15 weeks, respectively; and of whole-body exposure to 300 ppm of vinyltoluene for 6 h daily, 5 days a week for up to 21 weeks. Exposure to 100 ppm of vinyltoluene did not cause any significant impairment of tail nerve function throughout the 21-week exposure period. Significant changes in MNCV and SNCV were consistently observed from weeks 4 and 2, respectively, in 2,5-HD-treated rats. Changes resulting from exposure to 300 ppm of vinyltoluene were reported intermittently from week 15. Significant linear relationships were established between the length of treatment with 2,5-HD, length of exposure to 300 ppm of vinyltoluene, and the extent of impairment of tail nerve function. Structural damage to the sciatic nerves was only seen in 2,5-HD-treated rats. It is concluded that vinyltoluene can be regarded as an airborne chemical which leads to the development of a borderline experimental neuropathy at a level of 300 ppm.