Grapefruit juice contain furanocoumarin derivatives which are known to interact with various drugs such as felodipine, leading to the increased bioavailability. Due to very low concentrations of furocoumarin in grapefruit juice, isolation of these compounds has been a challenge to researchers. Five grapefruit (Citrus paradisi Macf.) varieties such as `Marsh White', `Duncan', `Rio Red', `Orange Flesh', and `Mexican Red' were harvested and analyzed. Samples were extracted successively three times with ethyl acetate until all furocoumarins were extracted. The dried extract was reconstituted in methanol and used for quantification using high-performance liquid chromatography. Furanocoumarins were quantified by gradient elution with methanol and water as mobile phase with a flow rate of 1.1 mL/min at 240 nm. The concentrations of bergamottin, dihydroxybergamotin (DHB) and dimer of DHB were shown to distinctly differ among varieties. Red colored grapefruit showed lower concentrations of the furocoumarins compared to white colored grapefruit. Among the five varieties, `Rio Red' grapefruit contain lower concentrations of bergamottin and DHB. Further studies are continued to quantify other dimers and commercial varieties. Knowledge of furocoumarin levels in grapefruit may eventually help the consumer to make decision about eating grapefruit and/or drinking juice while taking certain medications.