Calprotectin (L1) is a major granulocyte and monocyte protein which is released during activation of these cells. The plasma level of L1 is thought to reflect disease activity in rheumatoid arthritis (RA). In our cross sectional study of 70 patients with RA, L1 had significant correlations with erythrocyte sedimentation rate (r = 0.50), C-reactive protein (r = 0.58), orosomucoid (r = 0.62), platelet count (r = 0.42), leukocyte count (r = 0.33) and IgM rheumatoid factor (r = 0.32); and with the following clinical variables: number of swollen joints (r = 0.24), grip strength (r = -0.22), PIP joint circumferences (r = 0.33) and a combined global assessment score (r = 0.24). L1 was higher in seropositive (median 14,861 micrograms/l) than seronegative patients (median 10,487 micrograms/l) (p less than 0.03).