Symptoms and signs in four patients with thalidomide-induced neuropathy developing during treatment of discoid lupus were limited for long period to distal paresthesiae with altered sensory conduction velocities. Semi-thin biopsy specimens of the distal sural nerve showed depopulation of myelinized fibers, mainly affecting those of large caliber, and signs of axonal degeneration. Study of dissociated fibers showed a high proportion of E fibers. Morphometry confirmed the axonal lesion. Ultrastructural examination demonstrated anomalies of axons of amyelinic fibers (vacuoles, lamellar figures) and of Schwann cells (stacked cytoplasmic prolongations), together with numerous collagen pockets, all non-specific lesions. The disease course was slow, with disappearance of sensory symptoms in a few weeks in 3 of the 4 cases and normal clinical findings in one of the four patients one year after cessation of treatment. Definite correlations between the dose administered and the severity of the neuropathy could not be established. The still poorly understood mechanism of action is discussed.