We report on 264 patients with operable breast cancer, treated between 1980 and 1984 at the First Clinic of Obstetrics and Gynecology in Vienna. The operation was in all cases a modified radical mastectomy. The patients were randomized in two groups. In one group of 140 patients, the lymphatic tissue of the axilla was marked by technetium-99 antimonsulfide and these patients were operated on a gammacamera. The other group of 124 patients was not marked. This unspecific imaging of lymph nodes enabled us to increase the average number of removed lymph nodes by 25% in the marked group. In this group the amount of lymph-node-positive cases was 50.7% compared to 37.4% in the unmarked group. This difference may find its explanation in the higher number of lymph nodes removed. All other prognostic parameters in both groups showed no significant difference. After an observation period of 5 years or longer no difference in survival rate, disease-free interval, local and regional recurrence or distant metastases was found. This seems surprising because the number of lymp-node-positive cases was higher in the marked group, which according to oncological principles should result in a lower prognostic score. The explanation may be that a higher number of identified and removed lymph node metastases may bring those patients the advantage of modern adjuvant therapy and therefore a better prognosis.