Although traditional teaching emphasises that 70-80% of patients with rheumatoid arthritis have positive serological tests for rheumatoid factor, a review of the evidence suggests that the seronegative group has distinctive characteristics. In a blinded and controlled evaluation of hand and wrist films we correctly identified the serological status of 43 out of 46 patients satisfying the ARA criteria for 'definite RA'. The radiographic appearances of the seronegative group differed significantly from those of the seropositive group in (1) degree of juxtalesional osteosclerosis (p less than 0.001); (2) the relative absence of classical subchondral erosions (p less than 0.001); (3) presence of new bone formation (p less than 0.001); (4) more fusion (p less than 0.001); (5) more asymmetrical joint involvement (p less than 0.001); and (6) predominant carpal involvement (p less than 0.001). The nature of the destructive process, as defined radiologically, may be different in patients with seropositive rheumatoid arthritis from that seen in individuals with so-called 'seronegative rheumatoid arthritis'.