Dynamic T1-weighted FLASH MR imaging, obtained just after i.v. gadopentetate dimeglumine injection, and pre- and postcontrast T1-weighted spin-echo (T1-SE) MR imaging were performed to compare their information value with respect to inflammatory activity in immunoinflammatory gonarthritis. We examined 16 clinically active (CAG), 7 clinically inactive (CIG) and 4 healthy knees. The synovium of a preselected slice was outlined. Its area and relative signal intensity increase after gadopentetate dimeglumine on T1-SE and FLASH (at each time t) were calculated. The CAG knees showed a mean signal intensity increase on early dynamic FLASH images higher by far than the CIG knees, while no significant difference was found on spin-echo images obtained 5 to 15 min after contrast injection. The early signal enhancement probably reflects the perfusion and capillary permeability of the synovium. The area of synovium could differentiate between healthy and arthritic knees. Gadolinium-enhanced dynamic FLASH imaging may provide clinically useful information about the actual inflammatory activity of arthritic joints.