['To determine daily production of nitric oxide (NO) measured as urinary nitrate excretion, and the effect of prednisolone in patients with rheumatoid arthritis (RA).', 'Twenty four hour urinary nitrate was measured by gas chromatography in 10 patients with RA, before and two to four weeks after commencement of prednisolone 0.5 mg/kg body weight, and in 18 healthy controls.', 'Before the start of prednisolone treatment the urinary nitrate excretion in patients with RA was 2.7-fold greater (p < 0.001) than that in healthy volunteers. After prednisolone it decreased significantly, by 28%, at which time inflammatory activity (as indicated by C reactive protein, erythrocyte sedimentation rate, joint count, and early morning stiffness) was also reduced considerably. Despite this decrease, the urinary nitrate excretion in patients with RA remained twice that in the control group (p < 0.05).'] Is urinary nitrate excretion increased in patients with rheumatoid arthritis and reduced by prednisolone?