Two patients with infantile Refsum (phytanic acid storage) disease were treated at 9 mos and 5½ years of age with a low phytanic acid diet and the effects studied over a 2-yr period or longer in the Depts of Chemical Pathology, Neurology and Histopathology, Adelaide Children's Hospital, and the Dept of Neurology, Prince of Wales Children's Hospital, New South Wales, Australia. Elevated phytanic and pipecolic acid plasma levels were significantly decreased but very long chain fatty acids remained grossly abnormal after 6 wks or longer on the diet consisting of skimmed milk powder, white meats, fish, root vegetables, some fruits and supplementary vitamins. Growth, motor skills, self-mutilating behavior, intention tremor and nystagmus improved, although ataxia and hypotonia persisted in the older child who developed peripheral neuropathy with slowed motor and sensory nerve conduction velocities. Impaired visual acuity with optic atrophy and retinitis pigmentosa and sensorineural deafness persisted. Head growth continued at the original 25th and 3rd low percentiles. Electronmicroscopy of liver biopsies before and after dietary treatment showed an increase in inclusion bodies, and peroxisomes and lysosomes were present. [1]