Natural abundance in vivo13C NMR spectra were obtained from spores of three species of VA mycorrhizal fungi: Glomus intraradix Schenck & Smith, Glomus etunicatum Becker & Gerdemann and Gigaspora margarita Becker & Hall. The presence of trehalose was established in the spectra of Gl. etunicatum and Gi. margarita. HPLC analyses supported these observations and indicated that Gl. intraradix spores also contained small amounts of trehalose, not readily detectable by 13C NMR. Trehalose constituted between 0.06% and 1.6 %(w/w) of the spore dry weight, depending on the species. Only trace amounts of other sugars, including glycerol, were detected. An in vivo NMR time course experiment indicated that trehalose was readily utilized during spore germination.