The present invention relates to a method of enriching for membranous microvesicles relative to the cellular population in a biological sample. More particularly, there is provided a method for enriching for exosomes from plasma. In a related aspect, there is provided a method of reducing the concentration of cellular and cellular derived molecules in a biological sample. Still further, the present invention provides methods for selectively isolating mRNA subpopulations from exosomes. Yet further, there are provided methods of amplifying exosome derived RNA. The method of the present invention is useful in a range of applications including, but not limited to, diagnostic, prognostic, therapeutic, research and development applications, to the extent that the enrichment of exosomes is required.