In a prospective 24 week study of 25 patients with rheumatoid arthritis (RA) weekly intramuscular (IM) sodium aurothiomalate resulted in a small but significant reduction in the circulating lymphocyte count. Analysis of absolute levels of pan T cells, T4 helper cells, T8 suppressor cells, T4/8 ratio, B cells, and major histocompatibility complex (MHC) class II positive cells showed reductions in these subsets, though these changes did not reach significance. At entry there was no association between circulating lymphocyte counts and subsets and clinical and laboratory indices which reflected disease activity, and during the study gold responders could not be differentiated from non-responders with regard to changes in lymphocyte counts and subsets. Thus this study suggests that weekly IM gold leads to a modest reduction in circulating lymphocyte numbers which involves most subsets. This effect appears to be independent of the clinical efficacy of this drug.