Mammography and physical breast examination are currently the most frequently and recognized screening tools for detection of breast carcinoma. These methods have been proved successful for early detection of breast cancer. Considering the 85% sensitivity associated with combined mammography and physical examination and a low positive predictive value of 20%-30% for diagnosis of breast carcinoma, there is a critical need for a more accurate, noninvasive imaging test to improve the sensitivity and specificity of mammography (7, 19, 20). Since early 1992, we have studied over 1200 women with clinically and/or mammographic abnormalities prior to breast biopsy and/or fine needle aspiration cytology of the breast. We have evaluated the role of Tc 99m Sestamibi as a complimentary procedure to conventional mammography in detection of breast carcinoma. The preliminary results of our studies have been published elsewhere (14, 17, 18). DuPont Merck Pharmaceutical Company in the USA on that basis, determined to conduct a multicenter clinical trial for the role of this radiopharmaceutical for the diagnosis of breast carcinoma in women with mammographically and/or clinically palpable abnormalities. This study was conducted at 42 institutions throughout the United States and Canada enrolling 673 women who where otherwise scheduled for breast biopsy and/or mastectomy. The preliminary results of this trial in both palpable and nonpalpable breast abnormalities are encouraging (24). Our most recent study on 157 women (mean age 47.9 years +/- 10.2) with 164 lesions with indications for histologic and cytologic analysis who underwent scintimammography with Tc 99m Sestamibi demonstrated the sensitivity of 92.3% and the specificity 87.5% (15). We have concluded that Scintimammography with Tc 99m Sestamibi can be used in conjunction with mammography to improve its specificity.