The aim of the present study was to assess serum pro-matrix metalloproteinase-3 (proMMP-3) as a marker of disease activity in rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) patients. The study included 28 RA patients with disease duration < 2 years, 24 RA patients with disease duration >2.5 years, 24 SLE patients and 12 healthy controls. Patients were evaluated and hand X – rays were done for all RA patients. Serum proMMP-3 was measured for patients and controls by ELISA. Serum proMMP-3 was elevated in the sera of all patient groups in comparison to controls and correlated with some manifestations of disease activity and radiologic progression in RA but not with disease activity in SLE.