Seventy-two patients with relatively early but progressive rheumatoid arthritis were treated with chloroquine sulphate, D-penicillamine or a combination of both drugs over 1 year. Chloroquine resulted in significantly fewer side-effects but combined treatment appeared to increase the risks of toxicity. Significant clinical improvements were seen with each regimen and these were indistinguishable between treatments. However, chloroquine had less impact on haemoglobin, ESR, rheumatoid factor levels and C-reactive protein than the other treatments. Furthermore, radiological deterioration was most frequent amongst those given chloroquine alone. Combination treatment with D-penicillamine and chloroquine thus offered no advantages. Chloroquine caused fewer side-effects than both D-penicillamine and combination treatment but appeared to have a less pronounced effect on the disease process as measured by laboratory and radiological indices.