Clinical and laboratory measurements taken at the onset of rheumatoid arthritis in 149 patients were compared with the severity of radiological changes seen at 3 years in the hands and feet, and cervical spine. The strongest association with the severity of peripheral radiological damage was rheumatoid factor (p less than 0.0001 for both the latex titre and RAHA titre). Subluxation of the cervical spine was associated only with the presence of HLA-Dw2 (p less than 0.02) and HLA-B7 cross-reacting group (p less than 0.02). Discriminant function analysis utilizing latex titre, RAHA titre, haemoglobin level, and platelet count predicted the development of erosive or nonerosive disease in 79%. This method was less successful in predicting the actual severity of erosive damage and was not improved by the addition of HLA data. Radiological outcome in the cervical spine was successfully predicted in 82% using HLA-Dw2, HLA-B27 and age of onset of disease. It is concluded that the best predictors of erosive disease were standard laboratory features measured at onset, but that more powerful discriminant factors are needed if these are to influence clinical practice. Further prospective studies will establish whether rheumatoid involvement of the cervical spine is an expression of the influence of HLA determinants in this disease.