In an investigation of canine globoid leukodystrophy, cerebroside β-galactosidase activities were assayed in 24 brains from neonatal and older dogs and in 90 canine leukocyte pellets from nine samplings. The neonatal brains had significantly less enzyme activity than the brains of older dogs, which indicates a potential complication in making neonatal and fetal enzymatic diagnoses. For leukocytes, heterozygous activities averaged 51 percent and globoid leukodystrophy activities 18 percent of mean enzyme activity of normal leukocytes. Variability of leukocyte enzyme activities among the nine samplings was large, but within each sample, variability per genotypic category was moderate. A statistical model was developed to facilitate enzyme diagnosis in the dog and, by implication, in human globoid leukodystrophy and other sphingolipidoses.