Somatostatin-receptor (SS-R) scintigraphy successfully shows primary cancers and distant metastases in most patients with carcinoids, islet cells tumours, and paragangliomas. Previous in-vitro studies indicated that somatostatin receptors are present in human breast cancers. We report positive scintigraphy with [111In-DTPA-D-Phe1]-octreotide in 39 of 52 primary breast cancers (75%). Parallel in-vitro autoradiography with [125I-Tyr3]-octreotide of 30 of these showed a corresponding somatostatin-receptor status in 28. Significantly more invasive ductal cancers could be shown than invasive lobular carcinomas (85% vs 56%; p < 0.05). Also the number of T2 cancers which were shown was higher than T1 (86% vs 61%; p < 0.05). Imaging of the axillae showed non-palpable cancer-containing lymph nodes in 4 of 13 patients with subsequently histologically-proven metastases. In the follow-up after a mean of 2.5 yr, SS-R scintigraphy in 28 of the 37 patients with an originally SS-R-positive cancer, was positive in the 2 patients with clinically-recognised metastases, as well as in 6 of the remaining 26 patients who were symptom-free. Raised carcinoembryonic antigen (CEA) and CA 15-3 values were observed in only 2 and 1, respectively, of these patients. Most primary breast cancers can be shown by SS-R scintigraphy, especially invasive ductal cancers. This technique may be of value in selecting patients for clinical trials with somatostatin analogues or other medical treatments. Furthermore, SS-R scintigraphy is more sensitive than measurements of the usual serum cancer markers for detecting recurrences of SS-R-positive breast cancer.