The authors studied the immunitary responses to Levamisole in a group of patients recently operated for bronchogenic carcinoma. The results were compared with those obtained from two other groups, i.e. one of patients recently operated of bronchogenic carcinoma but not treated with Levamisole and another one of patients recently operated for a non-neoplastic disease and also not treated with Levamisole. All subjects underwent a similar investigation of the cell-mediated and the humoral immunity parameters at the beginning of the study and after 30 days. The comparison of the results showed a depression of the cell-mediated immunity in the patients operated for bronchogenic carcinoma. This depression subsided more promptly in patients submitted to Levamisole therapy. This effect was achieved particularly through a better blastogenic responsiveness to the PHA and an enhanced Rosettes E forming. The use of Levamisole in the pre- and post-operative period is thought to be beneficial in order to avoid distant recurrences. This effect is obtained by a stimulation of host defense mechanisms.