The knees of 20 patients with rheumatoid arthritis and two healthy volunteers were evaluated with magnetic resonance (MR) imaging. Spin-echo sequences were performed, and the signal-intensity patterns of normal and pathologic articular soft-tissue structures were quantitatively evaluated with a dynamic FLASH (fast low-angle shot) sequence after bolus intravenous injection of gadolinium diethylenetriaminepentaacetic acid. In contrast to the spin-echo images obtained before injection of contrast material, it appears possible with this technique to distinguish joint effusion from hypervascular pannus formations and to grade the vascularity of proliferative synovitis. Flat pannus deposits on the articular surface and subchondral pannus masses were identified only by their marked enhancement of signal intensity after injection of contrast material. Dynamic MR imaging appears to yield decisive information for diagnosing rheumatoid arthritis.