A group of 11 B27-positive, seropositive patients with rheumatoid arthritis was compared with 11 matched B27-negative seropositive patients. The radiographs of all limb joints, the sacroiliac joints, and the cervical spine were read blindly. Ten patients in each group were radiographed 2-6 times during observation periods of 3-13 years; one patient in each group was only examined once. The prevailing picture of both groups was that of progressive erosive rheumatoid arthritis, although two small differences were found: Erosions of the apophyseal joints of the cervical spine and slight periosteal new bone formation of the shoulder, hip, and knee regions occurred more often in the B27-positive than in the B27-negative group.