Ten commercial standardized Ginkgo biloba extracts were examined for flavonol glycoside and terpene lactone content. All samples arrived with certificates of analysis stating that the extracts were standardized Ginkgo biloba leaf extract and that they contained a minimum of 24% total flavonol glycosides and 6% terpene lactones. Samples were analyzed for total flavonol glycosidesusing a method involving acid hydrolysis and subsequent quantification of the flavonol aglycones by HPLC coupled with UV diode array absorbance detection. Analysis of intact flavonol glycosides and terpene lactones was accomplished using HPLC coupled with UV diode array detection and electrospray mass spectrometric detection. Of the ten standardized extracts eight samples provided chromatograms and chemical values characteristic of previously published analyses of ginkgo leaf extracts. One sample provided analyses that suggested that the extract had been adulterated with rutin in order to elevate total flavonol glycoside levels. Another sample indicated that it was not an extract of Ginkgo biloba leaf at all. Adulteration with rutin was not strongly evident when the acid hydrolysis method was used to analyze the sample for total flavonol glycosides. However, this particular adulteration was easily evident when analyzing the samples for characteristic intact flavonol glycosides. This work demonstrates the need for extensive quality control analyses for herbal products and that the analysis of intact characteristic compounds provides a reliable method for detecting adulteration.