Mammography and physical examination have a sensitivity of 85 percent for detection of carcinoma of the breast. Mammography also has a positive predictive value of 15 to 30 percent. The aim of this study was to evaluate the usefulness of scintimammography (SMM) as a screening technique for the detection of carcinoma of the breast and compare the test's sensitivity and specificity with that of mammography. We conducted SMM on 59 female patients in whom abnormal mammogram and physical examination warranted biopsy of the breast or fine needle aspiration cytology of the breast, or both. Each patient received 20 millicuries of 99mTc Sestamibi intravenously. Five and sixty minutes postinjection, planar breast images in lateral and posterior oblique views were obtained. In 23 patients with biopsy-confirmed carcinoma of the breast, the SMM result was positive. In 33 patients with benign breast lesions, no increased uptake of Sestamibi was noted in the breast. Five other patients with benign lesions of the breast had false-positive scans. There was one patient with an intraductal carcinoma and a cluster of microcalcifications on mammography without an associated mass, for whom the 99mTc Sestamibi scan was negative. In the group of patients studied, the sensitivity of SMM was 95.8 percent, specificity was 86.8 percent, positive predictive value was 82.1 percent and, most importantly, the negative predictive value for the detection of carcinoma of the breast was 97.1 percent. We conclude in this pilot study that SMM is a highly sensitive test that improves the specificity of conventional mammography for the detection of carcinoma of the breast and deserves further study as a screening technique to potentially reduce the number of mammographically "indicated" biopsies of the breast that yield negative results for carcinoma.