Mononuclear cells from peripheral blood and draining lymph nodes of 40 patients with invasive locoregional breast cancer were examined for immunological cell surface markers (E, EAhuman, EAox, EAC, SIg pos.). Concomitantly, blood lymphocytes from 36 healthy women and axillary and mesenteric lymph-nodes from patients without malignant diseases were tested as controls. In peripheral blood of tumor patients E rosette-forming cells were slightly diminished as compared to the control group, whereas EAox and EAC rosette-forming cells were increased. These differences may be age-dependent rather than tumor-related. In the draining lymph nodes of breast cancer patients as well as in the control lymph nodes, the percentages of EAC rosette-forming cells and SIg positive lymphocytes were significantly increased compared to peripheral blood, whereas E and EAhuman rosette values remained unchanged. Percentages of EAox rosettes on the other hand were strongly diminished in the draining lymph nodes, suggesting that the EAhuman and EAox rosetting techniques detect 2 types of Fc-receptor bearing cells. No significant differences were found between the cell surface marker analysis of tumor-free and metastatic lymph nodes of breast cancer patients and the control lymph nodes.