The distribution of T lymphocyte subsets was determined in peripheral blood (PB) of two groups of patients with rheumatoid arthritis by using monoclonal antibodies (OKT). In untreated patients the percentage of OKT4+ cells (helper/inducer) was found to be significantly increased as compared to healthy controls. In patients receiving oral gold therapy a similar increase in OKT4+ cells was confirmed; furthermore, these patients showed a significant decrease in OKT8+ cell population (cytotoxic/suppressor) compared to untreated patients and to normal controls. A small numerical superimposition of values of OKT4+ and OKT8+ lymphocytes was observed in untreated but not in treated patients.