Background: The aim of the study was to investigate whether pre-therapy vascular delivery assessment [using dynamic contrast enhanced magnetic resonance imaging (DCE-MRI)] can predict reduction in breast cancer metabolism [detected using 2-[F-18] fluoro-2-deoxy-D-glucose positron emission tomography ((18)F(-)FDG-PET)] after a single cycle of chemotherapy. Reduction in F-18-FDG PET metabolism has previously been shown to correlate with histological response to primary chemotherapy. Patients and methods: Seventeen patients with large or locally advanced invasive ductal carcinomas of the breast were imaged using DCE-MRI and F-18-FDG-PET prior to therapy and 20 days after the first cycle of chemotherapy. MRI data were analysed using a multi-compartment model. PET data were analysed using standardised uptake value (SUV) analysis. Results: A significant association (P < 0.05) was observed between pre-therapy DCE-MRI vascular parameters and the reduction in PET metabolism resulting from administration of one cycle of chemotherapy. Conclusions: A relationship was demonstrated between pre-therapy DCE-MRI vascular parameters and the reduction in PET metabolism after a single cycle of chemotherapy. This suggests that reduction in PET metabolism as a result of chemotherapy may be dependent, at least in part, on pre-therapy vascular delivery. These pre-therapy vascular characteristics may be suitable for use as a surrogate measure for initial chemotherapy delivery, a key factor in chemotherapeutic efficacy.