Neurospheres from adult mouse subventricular zone (SVZ) were grown in suspension cultures for 12-15 days. Neurospheres consisted mainly of neural precursor cells (NPCs) immunoreactive for nestin and also contained nestin-negative precursors. We used these neurospheres to determine the effects of synthetic beta-amyloid fragments (both betaAP(1-42) and betaAP(25-35)) on NPC proliferation, differentiation and survival. We show that neurospheres exposed to 25 microM betaAP(25-35) or betaAP(1-42) for 24 h (a toxic condition for mature neurons) did not undergo apoptosis. Instead, betaAP(25-35) orientated nestin-negative precursors towards nestin-positive NPCs and turned nestin-positive NPCs into neuroblasts. Intracerebroventricular infusion of full-length betaAP(1-42) increased the population of PSA-NCAM-positive cells in the SVZ, without affecting proliferation. We conclude that betaAP influences the fate of progenitor cells, driving their differentiation towards a neuronal lineage.