Angiogenesis is a common characteristic of tumours, and it is reasonable to assume that it has an influence on tumour growth, depending on the grade of malignancy. We therefore studied angiogenesis in 25 patients: 14 with glioblastoma multiforme and 11 with grade I meningioma. Our aim was to assess how angiogenesis conditions growth and necrosis. The patients underwent MRI with standard and perfusion sequences. We calculated the volume of each tumour; for the glioblastomas the solid portion was taken as the difference between the overall volume and the volume of any necrotic portion. In the glioblastomas, we found an inverse relationship between blood volume and the size of the tumour, whereas in the meningiomas there was of a direct relationship. These correlations confirm in vivo the knowledge about necrosis in glioblastomas and its relationship to their inadequate vascular network. On the contrary, grade 1 meningiomas show an equilibrium between their microcirculation and the cellular component.