The aim of this work was to study the topographic distribution and the morphological behaviour of nerve growth factor (NGF) primed spleen cells injected into the lateral ventricles of developing rat brain. Serial coronal brain sections showed that these transplanted cells acquire phenotypical characteristics similar to those of mast cells (MCs) and that they enhance local neovascularization. These results, together with the observation that these cells are located in proximity to the hippocampus, a brain tissue which contains one of the highest levels of NGF, provide a model for studying the relationship between NGF and MC differentiation and secretion.