The clinical features of four patients with retinitis pigmentosa, ataxia and peripheral neuropathy but with no increase in serum phytanic acid are reported. Three patients also had sensorineural deafness and radiological evidence of cerebellar atrophy. Nerve conduction studies revealed abnormalities of sensory conduction and normal or only mild slowing of motor conduction velocity. Sural nerve biopsy demonstrated a reduction in the density of myelinated fibres. There were no onion bulb formations. These cases clinically resemble Refsum's disease, but differ in having no detectable biochemical abnormality, and a peripheral neuropathy which is not hypertrophic in type. They may represent unusual cases of spinocerebellar degeneration.