In a previous study the hyperreactive lymphocytes in bronchial asthma (BA) have been documented by mitogen induced cell-mediated cytotoxicity (MICC). Since MICC was considerably low in patients receiving substantial doses of steroids, further investigation was conducted. BA patients were divided into three groups: the first was given daily steroids, the second was given steroids on alternate days and the third consisted of a longitudinal follow-up study on the same individual being on different doses of steroids. Mixture of blood lymphocytes, phytohemagglutinin and Cr51 labeled target cells (P815/DBA2) were incubated in ratio 10:1 for 12 hours. Subsequently the cytotoxic potential of effector lymphocytes was detected by measuring the Cr51 in the supernatant of reacting cells. It was observed that cytotoxic correction index (CCI = Patient/Control Cytotoxic Index) was significantly lower among those in the first group and when the dose of Prednisone or its equivalent exceeded 40 mg/day. Comparison of the CCI between patients from the first and second groups supports alternate day corticotherapy in BA. Considerable fluctuation of CCI was apparent in the third group. Selected high doses of steroids suppressed MICC. This effect is reversible and offers a new practical in vitro guidance for monitoring an adequate dose of steroids in vivo.