Although defective in the catabolic part of the Krebs cycle, dormant spores of Agaricus bispours display the full complement of the enzymes of this pathway, with the possible exception of the α-ketoglutarate dehydrogenase complex. This could, however, be functionally replaced by the enzymes of the γ-aminobutyrate shunt (i.e. glutamate dehydrogenase, glutamate decarboxylase, γ-aminobutyrate aminotransferase and succinate-semialdehyde dehydrogenase) that have been shown to occur in these spores. The possible identity of the metabolite causing the observed inhibition of succinate dehydrogenase is discussed. The results are compared with those obtained from other fungi.