We have studied the effects of the immunosuppressive agent Cyclosporin A (CsA) on the allogenic stimulation of human lymphocytes from 10 patients with progressive systemic sclerosis (PSS) and 10 healthy controls, when activated in vitro during 1ry and 2ry MLR. CsA markedly suppressed 1ry MLR in both PSS subjects and controls. In contrast to the marked suppression of 2ry MLR observed for most of the PSS subjects and all control subjects, lymphocytes from 3 out of 10 PSS patients had paradoxically amplified allogenic responses when primed in the presence of CsA. The possibility is discussed that in these patients the recruitment of suppressor-effector cells by CsA-resistant suppressor-inducer lymphocytes is impaired.