The introduction of an automated flow cytofluorograph has facilitated the detection of T lymphocyte subsets because it enables a larger number of cells to be analyzed. Many authors have reported a decrease of cytotoxic/suppressor T lymphocytes in rheumatoid arthritis (RA), in contrast to the results of other workers. We believe that the discrepancy between the various studies is due to the fact that different methods and different criteria for patient selection were used. Our study comprised a larger number of patients which makes the results suitable for statistical inference. Disease activity is clearly defined and all drugs that could alter the results were excluded. The use of a flow cytometer enhances the reliability of T lymphocyte subset determination by monoclonal antibodies (OKT series). Our study confirms the reports, which suggested that the number of suppressor/cytotoxic T lymphocytes (OKT8+ cells/mm3) is decreased in patients with active RA, resulting in a high T helper/inducer lymphocyte/T suppressor/cytotoxic lymphocyte ratio (OKT4+:OKT8+). This immune balance represents an interesting feature of the disease, since several active antirheumatic drugs share a common immunomodulatory action, which normalizes the OKT4+:OKT8+ ratio. Finally, we found a good correlation between the OKT4+ cells and OKT8+ cells in the normal control population. This observation enabled us to isolate a subgroup of active patients with RA not responding to slow acting antirheumatic drugs and characterized by a low OKT4+:OKT8+ ratio.