The use of screening mammography has increased dramatically, leading to the discovery of suspicious, nonpalpable mammary lesions. Mammographic wire localization (MWL) is currently being used to facilitate the biopsy of these lesions. We reviewed 104 patients undergoing 106 biopsies after MWL during a 14 month period to determine the usefulness of MWL. The average age of the patients was 58 +/- 14 years, with a range of 38 to 83 years. Abnormal mammographic findings consisted of microcalcifications (48 per cent) or mass and density (43 per cent), or both (9 per cent). Lesions of the right side (55 per cent) and upper and outer quadrant (49 per cent) were predominant. An average of 1.4 (range of one to four) specimens taken at biopsy per patient were required to remove the lesion. The mean duration of the biopsy was 34 minutes, with a range of ten to 75 minutes, and the mean total time in the operating room was 63 (range 31 to 115) minutes. The average cost of the procedure did not differ significantly between local and general anesthesia ($1,030 versus $1,142, respectively). Pathologic findings included fibrocystic disease (77 per cent), carcinoma (12 per cent) and fibroadenoma (7 per cent). Normal mammary tissue was found in 4 per cent of the biopsies. Five of the 13 carcinomas were in situ and seven were either in situ (five) or microinvasive only (two); only six lesions were frankly invasive. Ten patients were treated with modified radical mastectomy while three had segmental resection. All patients had in situ or Stage I carcinoma. MWL effectively localized nonpalpable mammary lesions and allowed accurate diagnosis and treatment of early stage carcinoma of the breast.