The purposes of this study were 1) to investigate the feasibility of using optical tomography in the near-infrared (NIR) spectrum combined with ultrasound (US) localization (NIR/US) in monitoring tumor vascular changes and assessing tumor pathological response during chemotherapy and 2) to compare the accuracy of NIR/US with magnetic resonance imaging (MRI) in predicting residual cancer after neoadjuvant chemotherapy. Eleven female patients were studied during treatments with a combined imager consisting of a commercially available US system coupled to an NIR imager. Contrast-enhanced MRI was performed before treatment and surgery. Tumor vascular content was assessed based on total hemoglobin concentration and volume obtained from NIR data. A percentage blood volume index (%BVI) was calculated as the percentage ratio of the product of total hemoglobin concentration and volume normalized to pretreatment values. At treatment completion, pathologic assessment revealed three response groups: complete or near-complete responders (A), partial responders (B), and nonresponders (C). The mean %BVIs of groups A, B, and C at the treatment completion were 29.1 +/- 6.9%, 46.3 +/- 3.7%, and 86.8 +/- 30.1%, respectively (differences statistically significant, P < .04). At the end of cycle 2, the %BVI of group A was noticeably lower than that of the partial (P = .091) and nonresponder groups (P = .075). Both NIR/US and MRI were equally effective in distinguishing different response groups in this pilot study. Our initial findings indicate that NIR/US using %BVI can be used during chemotherapy to repeatedly monitor tumor vascular changes. NIR/US also may evaluate pathologic response during treatment allowing for tailoring therapies to response.