Previous studies have shown that an electromagnetic field (EMF) induces anti-inflammatory effect in arthritic patients. In order to understand the mechanism that reduces inflammatory changes in the joint, we studied the effect of EMF on adjuvant-induced arthritis (AIA) in rats. A well characterized model that resembles rheumatoid arthritis in humans, AIA was induced in male albino rats by the intradermal injection of Complete Freund's Adjuvant in the right hind paw. A Fransleau-Braunbeck coil system was used and a frequency of 0.5 Hz and magnetic field of 1,000 nT were found to be beneficial in reducing the hind paw swelling. The activities of myeloperoxidase in bone and of lysosomal enzymes (acid phosphatase and cathepsin D) in both serum and bone of arthritic rats were significantly higher than in the control rats. The enzyme activities in serum and bone declined significantly in the arthritic group exposed to the EMF. This preliminary study indicates that EMF is a potential therapy for the treatment of arthritic patients.