The influence of sodium aurothiomalate on the secretion of immunoglobulins by normal human lymphocytes in vitro was investigated by means of a reverse hemolytic plaque forming cell (PFC assay, Aurothiomalate inhibited the FFC response induced by pokeweed mitogen (PWM) and by Epstein‐Barr virus (EBV) in a dose dependent manner. The inhibition was irreversible, as pre‐incubation for 2 h with the drug followed by extensive washing and further culture in gold salt–free medium still caused an inhibition of the PFC response to PWM and to EBV. Cell proliferation was not significantly affected, suggesting that the inhibition of PFC formation was not due to cytotoxicity. Pre–incubation of monocytes/macrophages (Mø's), T lymphocytes and B lymphocytes with the gold compound prior to culture with PWM showed that M0's and B cells were highly sensitive, whereas T lymphocytes where resistant to the drug. The findings indicate that aurothio‐malate inhibits the polyclonally induced PFC response by interfering with accessory Me function and by affecting the B lymphoc