A highly sensitive method for measuring endogenous phylloquinone and menaquinones in animal tissues was developed, based on high-performance liquid chromatography with coulometric reduction and fluorimetric detection, following extraction from tissue homogenate and purification on a Sep-Pak silica cartridge followed by thin-layer chromatography. The detection limits of phylloquinone, menaquinone-4, -6, -10 and -13 were 40, 40, 50, 70 and 80 pg/g in rat liver, respectively.