An analytical method for the determination of lycopene in tissues and plasma of rats is described. The method was validated for the determination of lycopene in liver and plasma with respect to selectivity, linearity, accuracy, recovery and precision. Following precipitation of proteins with water-ethanol plasma was extracted with hexane; tissues were extracted with acetone followed by precipitation of proteins with water-ethanol and extraction of lycopene with hexane. Separation and quantification of geometrical isomers of lycopene was achieved by normal-phase HPLC with UV/VIS detection at 471 nm. The method proved to be selective and specific for lycopene in plasma and liver. Detector response was linear in the range from 2 ng/g to 10 microg/g liver and 0.5 ng/ml to 2 microg/ml plasma, respectively. Average recoveries ranged from 96 to 101% in spiked liver samples and from 91 to 94% in spiked plasma samples. Intra-day variability (C.V.) was < or = 6% and < or = 5% in liver and plasma, respectively. Inter-day precision was < or = 9% for liver samples and < or = 6% for plasma samples. The procedures were successfully applied to the sample analysis of pharmacokinetic and metabolism studies.