An immunocytochemical method for the detection of cancer cells, in the cell suspension obtained by scraping the surface of the surgical resection margins is described and its sensitivity compared to the conventional histology performed on random biopsies from the same margins. The reactivity of the cells with a pool of monoclonal antibodies (Mab) directed against epithelial markers indicated that in 80% of the 42 cases tested, the scraping method was adequate for the gathering of cells from the margins. The analysis of the samples using B72.3 Mab specific for tumor cells revealed that, among B72.3-positive tumor cases, 31% of breast margins contained tumor cells, whereas only 12% were histologically positive. Our results indicate that the immunocytological methodology is therefore more sensitive and should be used alongside histological examination to detect the tumor contamination in the surgical resection margins.