Recent evidence suggests that angiogenesis, as assessed by vascular density, may be an independent prognostic factor in breast carcinoma. The authors chose to examine this hypothesis further using two different methods, both using an immunohistochemical technique to assess vascularity. In the first, tissue sections from 93 patients with human breast carcinoma were immunostained for the endothelial antigen CD 34. Fields were selected at random in sections stained with the monoclonal antibody QBEnd/10, and both the number of blood vessels and percentage of endothelial cells per unit area measured using an interactive image analysis system (SEESCAN). In the second, an additional 72 patients were added and the 165 sections immunostained for CD31 (PECAM 1) using the monoclonal antibody JC 709. The area of highest vascular density was then identified and measured. A statistically significant correlation was found between percentage endothelial area and tumor type (P < .03) using the first method, and, for lymph node-negative patients only, between vascular density and tumor type (P < .02) using the second method. There was no correlation with lymph node status, recurrence, distant metastases, or overall survival using either method (minimum follow-up 12 years). The authors conclude that the evaluation of tumor angiogenesis using these methods does not provide additional prognostic information in this group of patients.