To study the relation of the newly discovered proinflammatory cytokine osteopontin (OPN) to lung fibrosis in patients with rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE), we selected 18 RA patients ( 7 ♂ and 11♀; 29.28 ± 10.42 years ) and 17 (6 ♂and 11♀, 37.7 ± 7.11 years) and 10 normal controls ( 27.3 ± 9.01 years). 7 of RA and 6 of SLE patients have clinical and radiological evidence of lung fibrosis. FEV1 % predicted, ESR, serum CRP and plasma osteopontin were measured. FEV1 % predicted was significantly lower in patients than controls and in those with fibrosis than in those without in both groups (p< 0.001 and