The presence and distribution of enzymes of polyphosphate (polyP) synthesis and degrActation was examined in mycorrhizal and non-mycorrhizal onion roots, and both external and internal hyphae of the endophyte, Glomus mosseae. PolyP kinase activity was detected in extracts of external hyphae and mycorrhizal roots. Activity was dependent on exogenous polyP and Mg2+, the reaction product being a long chain polyP. Exopolyphosphatase activity was detected in both mycorrhizal and non-mycorrhizal roots but activity was 134°O greater in the former. Endopolyphosphatase activity was also greater in mycorrhizal roots. Polyphosphatases were detected in extracts of internal hyphae, but not external hyphae. Polyphosphate glucokinase activity was demonstrated in extracts of external hyphae and mycorrhizal roots, the immediate reaction product being glucose-6-phosphate. These results are discussed in relation to potential mechanisms of P translocation and transfer in vesicular-arbuscular (VA) mycorrhizas. A novel technique for isolating the internal hyphae and associated vesicles and arbuscules from mycorrhizal onion roots is described.