Rats intoxicated with pure n-hexane, either by repetitive subcutaneous injection or by continuous inhalation, developed clinical and/or pathological evidence of peripheral neuropathy. Animals intoxicated by inhalation (400-600 ppm) developed clinical signs after forty-five days and displayed giant axonal swellings and fibre degeneration both in the central and peripheral nervous systems. The changes were most strking in tibial nerves supplying calf muscles and in selected areas of the cerebellum, medulla and spinal cord. In contrast to the usual picture associated with dying-back disease, the distal regions of proximal nerve fibres supplying calf muscles degenerated before equivalent regions of longer fibres supplying the hindfeet. The relevance of the central nervous changes to individuals recovering from toxic neuropathies and the need for a reduction of the present Threshold Limit Value (500 ppm) for human exposure are discussed.