We describe a reversed-phase HPLC method that uses gradient elution and diode array detection to quantitate eight biologically active phenolic constitutions of wine: the cis and trans isomers of resveratrol and their glucosides, catechin, epicatechin, quercetin, and rutin. ODS Hypersil served as the stationary phase; the gradient was formed by acetic acid, methanol and water. Each analysis required an equilibration period of ten minutes and a run time of fourty minutes for completion. Satisfactory peak resolution was achieved following direct injection of a 20-muL sample, and validation was accomplished by on-line spectral comparisons with known standards. Excellent linearity was obtained for all constituents, and the detection limits ranged from 30 mug/L (trans-resveratrol) to 1.5 mg/L (catechin). Recoveries approximated 100% range (95.2-105.5%), and the method provided good precision, with coefficients of variation between 1.17 and 3.38%. All of the phenolics measured were reasonably stable in opened wines protected against sunlight for up to 1 week at room temperature or 4 degrees C, but most showed losses of 10-40% when stored for 6 weeks at either temperature.