1. Mucopolysaccharides were analysed in the urine of thirteen patients with Morquio's syndrome aged between three and fifty-nine years and of fourteen controls of comparable ages.

2. There were no significant qualitative or quantitative differences between patients and controls.

3. The clinical and radiological findings suggested that these patients did not have the "Morquio-Ullrich" form of the disease, which appears on retrospective assessment of case reports to be more uniform and less diffuse than the Morquio-Brailsford form which may include a number of possibly unrelated diseases.

4. Keratosulphate has so far been demonstrated in the urine only of patients with the "Morquio-Ullrich" form of the disease, although the mucopolysaccharide excretion has been investigated in only a few patients with the Morquio-Brailsford form. The normal mucopolysaccharide excretion of the present series of patients suggests that a normal mucopolysaccharide excretion distinguishes the Morquio-Brailsford from the Morquio-Ullrich form, the latter having a number of features overlapping with Hurler's disease, where large amounts of mucopolysaccharide other than keratosulphate are excreted.

5. Both qualitative and quantitative analysis of urinary mucopolysaccharide are thus necessary to distinguish between Hurler's disease, the Morquio-Ullrich form and the Morquio-Brailsford's form of Morquio's syndrome.