Technical Abstract: To help meet the needs of consumers, producers of dietary tea supplements, and researchers for information on health-promoting tea compounds, we compared the following conditions for the extraction of tea leaves and green tea-containing dietary supplements: 80% ethanol/water at 60 'C for 15 min and boiled water for 5 min. The following 7 catechins, 4 theaflavins, and 3 alkaloidswere separated in a 70-min single HPLC analysis: (')- epigallocatechin, (')-catechin, (+)-epicatechin, (')-epigallocatechin-3-gallate, (')–gallocatechin-3-gallate, (')-epicatechin-3-gallate, (')-catechin-3-gallate, theaflavin, theaflavin-3-gallate, theaflavin-3_-gallate, theaflavin-3,3_-digallate, caffeine, theobromine, and theophylline. The following ranges of concentrations of flavonoids (catechins plus theaflavins) in the tea leaves extracted with 80% ethanol were observed (in mg/g): in 32 black teas, 19.8 to 115.1; in 24 green teas, 12.3 to 136.3; in 14 specialty teas, 4.9 to 118.5; in 7 herbal teas, 0 to 46.0. Total alkaloids in all teas ranged from0 to 32.6 mg/g. significantly greater amounts of flavonoids were extracted from the tea leaves with aqueous ethanol than with boiled water. Levels of tea catechins in 10 capsules sold as dietary supplements were about 50 to 75% lower than the amounts listed on the labels. Catechin content of 4 commercial green tea extracts ranged from 96 to 696 mg/g. The results make it possible to maximize the extraction of tea compounds to better relate the flavonoid and alkaloid content of teas and dietary tea supplements to their health-promoting effects.