Ultrastructural characteristics of the granulomatous reaction in the lymph nodes draining a female breast carcinoma are reported. The lesions shared the appearances of the epithelioid cell granulomas found in systemic sarcoidosis and in other granulomatous diseases, which were all excluded by thorough clinical investigation. The previous literature is briefly summarized, and the development and significance of this peculiar reaction in cancer-draining glands discussed with special emphasis on macrophage-lymphocyte interactions in the immune response.