Interactions between grapefruit juice and medications have long been recognized. In recent years, several furanocoumarins (FCs) that inhibit P450 activity in intestinal microsomes have been isolated from grapefruit juice. FCs, i.e., bergamottin (BG), bergapten (BP), bergaptol (BT) and 6',7'-dihydroxybergamottin (DHB), in samples was extracted with acetonitrile, and separated on a Phenyl column using 0.1% phosphoric acid-acetonitrile gradient as a mobile phase, with monitoring at 311 nm. The recoveries of BG, BP, BT and DHB from lemon juice spiked at the level of 5.0 microg/g were 103+/-0.7%, 99.5+/-0.2%, 96.5+/-0.2% and 90.1+/-0.2%, respectively. The quantification limits were 1.0 microg/g in samples. The contents of BG, BP and DHB in grapefruit juice (n=13), citrus fruit of 20 species and health food (n=16) were measured. The contents of BG were 0-16 microg/g, 0-16 microg/g and 0-5.6 microg/g, BT were 0-39 microg/g, 0-13 microg/g and 0-28 microg/g, DHB were 0-10 microg/g, 0-35 microg/g and 0-6.2 microg/g, respectively. BP was not detected. These results suggest that patients prescribed calcium antagonists or antiallergic agents should be cautions about their intake of FCs from grapefruit juice, citrus and health foods.