The microtiter plate reader has been used to obtain data on the inhibition of aldehyde dehydrogenase over a wide range of inhibitor concentrations. Multiple reactions can be run simultaneously and assayed rapidly with repetitive determinations of enzyme activity using this technique. The microplate reader allows for the efficient generation of concentration-inhibition curves of excellent precision, using only small amounts of material under uniform experimental conditions. The microplate reader can be very useful for pharmacologic studies which make use of spectrophotometric assays.