Beta-galactosidase-deficient siblings in two litters of English springer spaniel puppies showed a progressive neurological impairment, dwarfism, orbital hypertelorism, and dysostosis multiplex. An excess of GM1-ganglioside was found in the brain. Three abnormal oligosaccharides were present in samples of urine, brain, liver, and cartilage. Light microscopy of selected tissue specimens revealed cytoplasmic vacuoles in neurons, circulating blood cells, macrophages, and chondrocytes. Ultrastructural studies demonstrated that these membrane-bound vacuoles were of two types--one containing lamellated membranes and the other, finely granular material. These clinical and pathological findings are similar to those observed in human patients affected by the infantile form of GM1-gangliosidosis.