We found that the Dictyostelium orthologue of the Ras GTPase activating protein (RasGAP) Neurofibromin (NF1), a tumour suppressor that is mutated in the genetic disorder Neurofibromatosis type 1 (Xu et al., 1990), is a key regulator of both macropinocytosis and phagocytosis. This evidence concerns the gene NF1 and neoplasm.