This invention relates to stem cell microparticles, their use and production, in particular neural stem cell microparticles and their use in therapy. The stem cell microparticle is typicallyan exosome or microvesicleand may be derived from a neural stem cell line. The neural stem cell line may be a conditionally-immortalised stem cell line such as CTX0E03 (deposited at the ECACC with Accession No. 04091601).