OBJECTIVE Seventeen knees in 13 patients with rheumatoid arthritis (RA) were studied with MRI to clarify the dynamics of Gd-DTPA administered intravenously and to determine an optimal imaging time. METHODS Dynamic gradient recalled echo imaging with bolus intravenous injection of Gd-DTPA was performed following unenhanced T1- and T2-weighted SE imaging. Late-phase SE or serial gradient recalled echo images were obtained following dynamic study. RESULTS There was rapid enhancement of synovium with maximal enhancement ratio of 96-499% (mean 214 +/- 111%) with Tmax ranging from 120 to 660 s (mean 253 s). The synovial enhancement persisted over 80% of the peak enhancement for 6-27 min (average 12 min) with eventual enhancement of joint effusion from the periphery to the center beginning at 6 min to 8 min, 20 s after contrast medium injection. Complete enhancement of joint effusion was noted in four joints at 24-86 min. CONCLUSIONS We conclude that enhancement of synovium in patients with RA is a time-dependent phenomenon, and an optimal imaging time would be within 5 min following contrast medium administration.