Content and composition of glycosaminoglycans (GAG) was studied in leukocytes of 30 healthy persons and of patients with different types of myeloproliferative disorders: 32 patients with chronic myeloid leukemia (CML), 10 patients with polycythemia vera (PV), 5 patients with idiopathic myeloid fibrosis (IMF) and 10 patients with acute myelo blast leukemia (AML). The total content of GAG in healthy persons was 97.7 +/- 3.9 micrograms of uronic acid per 100 mg of dry cells, in CML and IMF it was 2-4-fold increased, in PV it was elevated by 20%, in AML it was diminished 3-5-fold. The elevated level of GAG in CML and IMF was due to presence of basophils and considerable quantity of immature cell forms: promyelocytes and myelocytes. In these cells changes in GAGs composition and their properties were shown: an increase of chondroitins deficient in sulfate groups and of heparan sulfate content, especially in basophils. The observed changes in GAG content and composition may be important for biological activity of the leukemic cells.