SUMMARYPolyphosphate was extracted from an Australian isolate oi Pisolithus tinctorius (Pers.) Coker & Couch, known to he mycorrhizal with Eucalyptus pilularis. It was separated from RNA and characterized hy PAGE and ^^F NMR spectroscopy. A broad pink hand, which showed y-metachromasy with toiuidine blue, ran faster on acrylamide gels than a number of purple-blue bands (various RNA fractions) and did not stain with ethidium bromide, was identified as polyphosphate. The major pink band co-migraied with a synthetic polyphosphate standard of a chain length of about 1 5 phosphate (PJ subunits, and analysis by ^^P nuclear magnetic resonance (NMR) spectroscopy confirmed that polyphosphate was a major fraction in the extract. Polyphosphate was extracted from mycelium grown at both high and low levels of P,, but the amount extracted from cultures grown with 10 mM P, (added as ammonium phosphate) was significantly greater, Polyphosphate was a substantial fraction of the phosphorus present in the hyphae and it is proposed that polyphosphate is transported along the hyphae by the motile tubule and vacuole system present in this fungus.