The excretion of acid mucopolysaccharides in the urine of seventy-seven patients was determined by the techniques described by Dorfman and by Berry and Spinanger. Eight of the patients had clinical and roentgenographic findings typical of either achondroplasia, Morquio's disease, Hurler's disease, or epiphysealis dysplasia multiplex, and eight others had non-specific abnormalities of enchondralbone formation. Forty-eight other patients in this study also had Legg-Perthes disease, slipped capital femoral epiphysis, or idiopathic scoliosis. There were thirteen normal controls. Only in the two patients with Hurler's syndrome was the urinary excretion of mucopolysaccharides elevated as determined by the methods used.