To determine the prevalence and clinical significance of leukocytosis in rheumatoid arthritis (RA), records of 98 consecutive outpatients with this disease were reviewed. Leukocytosis, defined as 2 or more white blood cell counts (WBC) greater than 10,000/mm, was found in 27%. Among patients currently receiving steroid therapy (mean dose prednisone 7 mg daily), the prevalence was 40%; in all others, the prevalence was 7.5%. The WBC elevation was primarily caused by an increase in neutrophils. Patients with leukocytosis tended to have more active arthritis, but there were no differences in extra-articular manifestations or drug therapy except for the use of corticosteroids.A review of the literature confirms the contributions of both disease activity and steroid therapy to WBC elevation. There is little published information on the effect of chronic, low dose corticosteroids on WBC counts, but our study suggests that this is an important factor in leukocytosis in RA.Newly detected leukocytosis in RA should alert the physician to the possibility of occult infection. In the absence of suggestive signs and symptoms, an infectious cause is seldom found, but, despite the few infections found in this series, continuing vigilance is recommended.