Biochemical anomalies in proband involved alterations in the spectrum of glycosaminoglycans (GAG) excreted with urine as well as a decrease in activity of lysosomal sulfatases (arylsulfatases A and B, heparan-N-sulfatase) in homogenates of leukocytes and cultivated fibroblasts. In healthy parents of the proband activity of the sulfatases was lower than in control donors but higher as compared with the proband. Antenatal diagnostics of mucosulfatidosis was carried out in fetus during the repeated pregnancy. The following biochemical anomalies were noted: alteration in the GAG spectrum in amniotic fluid, decrease in activity of lysosomal sulfatases in cultivated cells of the amniotic fluid. The pregnancy lead to a premature birth at 31st week of a girl. No alterations were observed in the spectrum of GAG's excreted with urine and in intracellular accumulation of 35S-GAG in the newborn child. Measurement of sulfatases activity in leukocytes enabled to identify conclusively that the child was a heterozygotic bearer mucosulfatidosis.