UDP-galactose:ceramide galactosyltransferase activity was assayed in the spinal cord and kidney of the recently discovered neurological mutant, the twitcher mouse, which is an enzymatically authentic model of human globoid cell leukodystrophy (Krabbe disease). The activity in the spinal cord was essentially normal during the early myelination period up to 15 days. There was a slight reduction at 20 days. At 25 and 33 days, the galactosyltransferase activity was drastically reduced compared to controls. In contrast, the galactosyltransferase activity in the kidney of twitcher mice remained normal throughout the developmental stages examined. Activity of the control enzyme UDP-glucose:ceramide glucosyltransferase was always normal in both the spinal cord and kidney. Thus, reduction of galactosylceramide synthesis occurs in the CNS secondarily to the pathological alteration of the oligodendroglia. No such reduction occurs in the kidney, at least for the last step of galactosylceramide synthesis. Reduced synthesis as the result of metabolic regulation in the presence of the catabolic block is therefore unlikely to be the cause of the lack of abnormal accumulation of galactosylceramide in the kidney of patients with globoid cell leukodystrophy.