In vitro studies were performed on joint tissues and fluid to evaluate the potential for nuclear magnetic resonance (NMR) in the study of joint disease. Values for spin lattice relaxation times, spin-spin relaxation times and mobile proton content were obtained on 51 consecutive whole synovial fluids (SF). Correlations were sought between NMR values and white blood counts, protein content, calcium, phosphorus, and diagnosis. Only a very weak correlation (0.444) was noted with total SF protein. Albumin added in vitro did produce good correlation (0.975). NMR values were not altered by the addition of monosodium urate, of calcium pyrophosphate, or hydroxyapatite crystals. In vitro measurements of dissected canine articular tissue showed differences in NMR between the different joint components and between inflamed and noninflamed tissues. Our findings suggest that estimation of the amount of inflammation by NMR values is not possible at this time, but with refinements of techniques, magnetic resonance imaging may provide superb images of articular soft tissue structures.