The ability of technetium 99m labelled nonspecific, polyclonal human immunoglobulin G (99mTc-IgG) scintigraphy to depict and quantify synovial inflammation was studied in patients with rheumatoid arthritis (RA). Eight patients with clinically active synovitis were injected with 350 MBq 99mTc-IgG, and imaging took place 4 h later. This resulted in excellent images of inflamed synovium. Significant correlations were observed between individual joint uptake on the scan and scores for joint pain (n = 316, p less than 0.001), joint swelling (n = 300, p less than 0.001) or the average of pain and swelling (n = 300, p less than 0.001). These results suggest that 99mTc-IgG scintigraphy may provide an objective, non-invasive test to detect and measure synovitis.