Antibody-dependent cell-mediated cytotoxicity (ADCC) exhibited by peripheral blood leukocytes was used as a criterion for assessing immune competence of groups of noncancerous individuals and of treated and untreated cancer patients. The results show that, as a group, leukocytes of nontreated cancer patients exhibited significantly lower ADCC than that exhibited by leukocytes of noncancerous individuals. However, the ADCC of leukocytes from cancer patients under treatment approximated that of normals. Thus, using ADCC as criterion, the results indicate that as a group, cancer patients under treatment tend to exhibit restored immune competence.