Comprehensive immune function by integrated score was assessed in 158 operable, 55 inoperable, and 52 metastatic breast cancer patients relative to 107 healthy controls. The score was derived from in vivo response to PPD and DNCB and in vitro lymphocyte stimulation by PPD and PHA. Proportion of E-RFC was significantly lower in patients than in controls but was not found to correlate directly with the above functional criteria. Fifty-one percent of the patients with early, operable tumors were shown to be at least partially immunosuppressed by integrated score achievement vs. 11% of controls. This proportion rises to 68% of inoperable and 89% of metastatic patients. Quantitative analysis by graded response revealed an additional, significant degree of immune impairment in the respective patient groups by all testing parameters. Depression of immune function in operable patients was not related to age nor influenced by surgery. Immunocompetence of patients with mammary dysplasia did not differ from controls. Increasing size of primary tumor (T) was not found to be matched by progressive degree of immunosuppression, excepting that associated with large T4 tumors. Patients with lymph node involvement (N+) were not significantly immunologically inferior to those without (N0) where the larger operable T2-3) tumors are concerned. In the smallest, T1 tumors, nodal involvement (N+) is accompanied by remarkable immunosuppression relative to T1N0 cases. This finding suggests a pre-existing immune defect inherent in T1N+ patients. It supports the hypothesis that the immunosuppression associated with early breast cancer is primary, patient related. Secondary tumor-induced depression of immune response characterizes advanced and metastatic human breast cancer.