12 women with primary breast cancer underwent somatostatin receptor scintigraphy (SRS) with 111In-DTPA-D-Phe1-octreotide. The tumour sizes varied between 2 and 5 cm and were all, except one, palpable at clinical examination. Tumour biopsies were taken with additional sampling from normal breast tissue, fat, muscle, axillary lymph nodes and peripheral blood. Ratios between the 111In activity concentration in the tissue biopsies (Ti) and in peripheral blood (B) as well as in normal breast tissue (Br) were calculated. In 8/12 patients the scintillation detector was used intraoperatively for radioactivity measurements of the biopsies in situ and ex vivo. The sstr-subtype profiles were determined by northern blot analysis and the relative expression of sstr2 by ribonuclease protection assay (RPA) and immunocytochemistry. Preoperative SRS visualised all primary breast cancer tumours. The scintigraphic image showed no correlation with the histopathological type of the tumour or with the abundance of oestrogen/progesterone receptors on the tumour. Two patients with a massive tumour infiltration of the lymph nodes had a distinct positive SRS of the ipsilateral axilla. In one patient with three nodal metastases the scintigraphic image of the axilla was weak but visible. Four other patients with a negative axillary scintigraphy had 1-2 lymph node metastases. The Ti/B ratios for the breast tumours varied between four and 33 and were not different from Ti/Br ratios. In lymph node metastases the Ti/B ratios were higher (10-41). Intraoperative detector measurements showed a significant difference between the breast tumour and normal tissue in 2/8 patients in situ. Similar measurements on excised tissues (ex vivo) showed a significant difference in 6/8 patients. Two patients with lymph node metastases exhibited a significantly increased uptake ex vivo by detector measurements, but in only one of them in situ. All tumour biopsies expressed the presence of sstrl, 3, 4 and 5, but not of sstr2 at northern analysis. On the other hand, sstr2 was detected in all tumours by RPA and immunocytochemistry. Preoperative SRS visualised primary breast cancer lesions in all 12 patients. SRS could also demonstrate extensive axillary tumour infiltration. Intraoperative use of the scintillation detector could not exclude axillary metastases in situ. The low Ti/B values of both primary tumours and metastases indicate limitations of the radiopharmaceutical used.