Two hundred and one patients (305 knees) with rheumatoid arthritis received intra-articular osmic acid in one or both knees. Assessment was based on pain relief, warmth, tenderness, size and presence of effusion, degree of synovial thickening and range of pain-free movement. Satisfactory results were obtained in 61% at one year gradually reducing to 22% over a five-year period. If only those knees with none or minimal joint damage were considered, then a satisfactory result was obtained in a higher percentage, 74% at one year and 38% at five years.