Lysolecithin has been used in many studies to induce demyelination in peripheral nerves. In the present investigation lysolecithin (lysophosphatidyl choline) was injected into rat sciatic nerves at a dose of 2-3 microns of a 10 mg/ml solution in order to study the effects of this lipid on cellular elements other than myelin within the nerve. Twenty-four hours after injection, there was splitting of myelin, lysis of Schwann cells, and complete loss of non-myelinated axons and their Schwann cells at the site of injection. Numerous swollen non-myelinated axons containing accumulated organelles were seen just proximal to the site of injection at 48 h. Loss of non-myelinated axons from the distal part of the nerve was also noted at 3 days after injection but 7 days regenerating non-myelinated axons had re-appeared in the distal part of the nerve. Although demyelination, followed by remyelination was prominent feature in the injected segment of the nerve, no damage to myelinated axons was detected. These results suggest that the presence of the myelin sheath protects the large myelinated axons against the action of lysolecithin, but with lysis of Schwann cells, the non-myelinated axons are exposed to the action of lysolecithin. Apart from selective damage to non-myelinated fibres with subsequent degeneration, it is also possible that lysolecithin interferes with axoplasmic flow in non-myelinated axons.