New MRI techniques such as the analysis of magnetization transfer or diffusion have provided evidence for subtle progressive alterations in tissue integrity prior to focal leakage of the blood-brain barrier (BBB) as part of plaque formation in multiple sclerosis. Since inflammation is capable of modulating the microcirculation, we investigated the hypothesis that changes in the local perfusion might be one of the earliest signs of lesion development. 20 patients with definite relapsing-remitting multiple sclerosis were analysed with regard to cerebral blood volume, cerebral blood flow, mean transit time and apparent diffusion coefficient (ADC), as well as conventional MRI parameters, on monthly follow-up scans. Among 89 gadolinium-enhancing lesions, we selected 18 that developed during the study and met strict inclusion criteria. In these, changes of perfusion parameters were detectable not only prior to the BBB breakdown, but also prior to increases in the ADC. Our data indicate that inflammation is accompanied by altered local perfusion, which can be detected prior to permeability of the BBB.