Antibodies raised against a glucose-containing tetrasaccharide-Glcalpha1-6Glcalpha1-4Glcalpha1-4Glc-coupled to KLH have been used in a radioimmunoassay to measure urinary excretion of the oligosaccharide in urine of patients with glycogenoses, pregnant women, and pediatric patients with soft tissue sarcomas. Preliminary data suggest that the rate of urinary excretion of this tetrasaccharide may be a useful indicator of the tumor mass present in certain patients. The hypothesis that the oligosaccharide may originate as a product of digestion of glycogen by amylase is under investigation.