A series of ascorbic acid and isoascorbic acid derivatives has been evaluated as inhibitors of malt, bacterial, fungal, pancreatic and salivary alpha-amylases using a simple and quick assay procedure. The results demonstrate that the enediol moiety of ascorbic acid is essential for alpha-amylase inhibition. Acylation of the primary and secondary alcohols, and the absolute configuration of the secondary alcohol, do not affect the potency of inhibition.