SummaryA method for isolation of sulfated acid mucopolysaccharides (AMPS) and corresponding mucoproteins from human urine by absorption on and precipitation with cetyltrimethylammonium bromide is described. After in vivo labelling with radiosulfur nearly all of the bound radioactivity was found in 2 fractions, one insoluble in 66% alcohol and the other soluble in 66% alcohol, but insoluble in 84% alcohol. The first is essentially free AMPS containing less than 10% protein while the second is a mucopolysaccharide-protein complex containing about 87% protein. Digestion of the second fraction with proteolytic enzymes yields a nondialyzable AMPS with about 26% protein. Chemical analysis indicates no other high molecular weight urinary substances are present in these preparations.