1. The uptake of a low dose of intravenously administered 99mTc over the distal and proximal interphalangeal joints was found to be lower in normal subjects than in patients suffering from rheumatoid arthritis, osteoarthritis and psoriatic arthritis. 2. The percentage uptake of technetium over the proximal and distal diarthrodial joints was significantly decreased in patients with rheumatoid arthritis by the oral administration of aspirin (4 g/day for 7 days) and it is proposed that this method may be of value in the routine assessment of anti-inflammatory drug therapy in rheumatoid arthritis.