Morquio B disease was found in a 15-year-old Japanese boy who presented with progressive generalized skeletal dysplasia without neurological manifestations. Mild keratan sulfaturia was found, and beta-galactosidase was deficient in fibroblasts. Gene analysis revealed two mutant alleles, 83Tyr-->His (Y83H) and 482Arg-->Cys (R482C). The former expressed a low enzyme activity (2-5% of normal), and the latter expressed no detectable enzyme activity.