The aim of this study was to evaluate changes in both size and contrast enhancement of breast tumors during neoadjuvant chemotherapy, using dynamic MRI with high temporal resolution. Patients with advanced breast cancer (n=21) underwent a 1.5-T MRI scan prior to and following neoadjuvant chemotherapy with four cycles. Dynamic contrast enhancement was measured using a fast turbo-FLASH sequence and quantified using a two-compartment model with the parameters k(ep) and amplitude. Image analysis was done on images overlayed with a color map of parameters. The correlation between tumor diameter measured by histopathology and MRI was 0.7 (p<0.003). A reduction of tumor size after chemotherapy of more than 25% was associated with a decrease of both analyzed contrast enhancement parameters (k(ep): p<0.002; amplitude: p<0.006), where k(ep) began to drop already after the first cycle of chemotherapy (p<0.008). A clear reduction of tumor size was only noted after the third cycle (p<0.008). In patients without tumor regression there was also a trend towards an early reduction of contrast enhancement. We assume that MRI with high temporal resolution and color mapping is a novel tool to assess therapeutic effects of neoadjuvant chemotherapy in breast tumors, which deserves further prospective evaluation.