A prospective study over one year of patients who had active rheumatoid arthritis discovered 64 who had received treatment for an adequate time with second-line drugs. In these patients there was evidence of continuing joint destruction as shown by radiological progression. During the year there were highly significant correlations between improvements in clinical and laboratory measurements, but neither group of tests was related to the degree of radiological change. However, in the second 6 months of treatment there was evidence that radiological progression was reduced. In a second prospective study of 88 patients with rheumatoid arthritis given prolonged, intensive therapy with second-line drugs and followed up for 10 years two-thirds showed radiological progression. However, the number of joints damaged per year fell significantly during the study period. There was a divergence between deterioration in radiological features and improvements in the ESR and functional capacity, though patients with a persistently low ESR had less radiological progression. These studies provide evidence that treatment may be associated with a reduced rate of radiological progression but suggest that changes in radiological progression and clinical and laboratory measurements may result from different mechanisms.