Pain threshold was measured in 106 patients with rheumatoid arthritis, 50 with ankylosing spondylitis, and 50 normal controls using Keele's algometer. In rheumatoid arthritis patients with a low pain threshold had more severe pain for a greater part of the day and required more tablets for pain relief. In ankylosing spondylitis the pain threshold was higher and was not related to pain or analgesic requirements. There was no evidence that pain threshold affected the course or outcome of rheumatoid arthritis in any way.