In vivo leukocyte migration in arthritis. We quantitated in vivo migration of neutrophils into the knees of patients with rheumatoid arthritis (RA) and osteoarthritis, using 99mtechnetium-hexamethyl-propylene-amineoxime-labeled leukocytes and gamma scintigraphy. Significant neutrophil migration occurred in patients with RA irrespective of disease duration, and it was reduced by 60% following intraarticular steroid injection. The reduction in neutrophil migration correlated with reduction in pain. Leukocyte migration into osteoarthritic joints was also demonstrated, although it was much less than that seen in rheumatoid joints. No significant leukocyte migration into the joints of patients without arthritis was demonstrated. This technique appears to provide a sensitive method for quantitatively assessing the neutrophil component of inflammation in individual joints of patients with arthritis. 