Fifteen out-patients with type I diabetes mellitus and microalbuminuria (mean +/- SEM: 95.4 +/- 13.9 micrograms/min), were administered the glycosaminoglycan sulodexide, with the aim of investigating its influence on the rate of albumin excretion. Sulodexide was given intramuscularly in a dose of 600 lipoproteinlipase releasing units/day for three weeks. Albumin excretion was measured before dosing, at weekly intervals during dosing and also during the subsequent follow-up period of six weeks. Sulodexide yielded a clear-cut and statistically significant lowering of albumin excretion after the first week of treatment (from 95.4 +/- 13.9 micrograms/min to 53.6 +/- 11.1 micrograms/min; p = 0.0055); albumin excretion was further decreased after three weeks of treatment (26.5 +/- 6.05 micrograms/min; p = 0.0007) and was maintained during the follow-up period, at the end of which the mean value was still significantly lower than at baseline (39.6 +/- 10.3 micrograms/min; p = 0.01). Sulodexide short-term administration did not influence the routine haematological, haematochemical and coagulative tests performed contemporaneously. Patients' compliance with treatment was very good and no adverse events were reported.