The capability of cyclodextrins to enhance greatly the solubility in water of poorly water-soluble substances makes them an ideal alternative for investigating the expression of enzyme activity with such substrates in aqueous solution. This capability is demonstrated by using soybean lipoxygenase with linoleic acid/beta-cyclodextrin and diethylstilbestrol/gamma-cyclodextrin, and cholesterol oxidase with cholesterol/methyl-beta-cyclodextrin.