We have developed a reversed-phase high-performance liquid chromatographic assay for the measurement of low nanogram levels of beta-carotene in a single sample of human buccal mucosa cells. The method includes a simple sonification step for cell disruption and release of the compounds into the supernatant. The limits of detection were 0.02, 0.02 and 0.07 ng/mg of protein for beta-carotene, retinol and retinol palmitate, respectively. Two patient populations were analysed. Average endogenous levels for beta-carotene normalized to protein were 0.25 ng/mg of protein (range 0.04-1.9 ng/mg, twelve patients). No evidence of endogenous retinol or retinol palmitate could be detected in the human samples. An oral dosing study of four normal individuals showed a wide variation of beta-carotene uptake. This rapid and sensitive method will enable investigators to use the non-invasive technique of buccal mucosa cell harvesting to determine cellular depot levels of beta-carotene in various patient populations.