Galactosylceramide beta-galactosidase cross reacting material was demonstrated 
in brain, liver, and skin fibroblasts from patients with Krabbe disease. The 
mutant enzyme was antigenically identical to the normal enzyme and exhibited 
similar electrophoretic mobility. Normal quantities of the catalytically 
deficient enzyme were measured in the patients' tissues by a sensitive single 
radial immunodiffusion assay, indicating that the mutation is in structural gene 
for the enzyme protein.