During the studies of regional lymph nodes originating from 50 patients with breast cancer, there were distinguished four stages in development of immune response. The first, stage of induction of the response concerned patients with non-infiltrating carcinoma. The second stage of the active immune response was observed in 1/3 of the patients with infiltrating cancer without metastases. In these cases, in the pattern of regional lymph nodes predominated medium sized lymphocytes within the thymus-dependent inner cortex, while in outer areas there was an increased number of small active follicles. Within the sinusoidal structures there predominated proliferating prohistiocytes growing in interaction with small lymphocytes. The third stage of immune response was characterized by weak activity and progressive cortical strophy of the lymph nodes and it was observed in 2/3 of the patients with invasive cancer. The fourth stage of immunologic response concerned the patients with minute-metastases within the regional lymph nodes. In these cases one group of the lymph nodes showed unstimulated pattern while the other a highly stimulated pattern with the presence of giant follicles.