The proposed plan is for the development of a needle biopsy and needle localization device that can be used with existing mammographic equipment. Using a stereotactic algorithm, this equipment will enable an operator to place a needle into the breast for obtaining aspiration cytology samples or prior to open biopsy, to place a localization wire within 1-2 mm in x, y and z. Since this method utilizes a computer and does not require photographic development, the entire process could be performed in a few minutes. In Phase II, research will be directed towards the development of prototype hardware and software that is suitable for experimental use in a clinical environment. Critical components will be selected and studied with the view of developing a cost effective device. The equipment will be tested on phantoms and patients to determine accuracy and ease of use compared with existing methodology.