The distribution of macular pigment stereoisomers in the human retina has been mapped and a pathway to account for the presence of the non-dietary carotenoid, meso-zeaxanthin, is proposed. Adult neural retinas were cut into three concentric areas centered on the fovea, and the extracted carotenoids were analysed and purified by high-performance liquid chromatography. The dicarbamate or dibenzoate derivatives of the collected zeaxanthin fractions for each tissue sample were further analysed by HPLC to determine their stereoisomer composition. Whole retinas from infant eyes were similarly analysed. The results show that, relative to zeaxanthin, the concentration of lutein in the adult neural retina increases with radial distance from the fovea while that of meso-zeaxanthin decreases. Infant retinas were found to have more lutein and less meso-zeaxanthin, relative to zeaxanthin, than adult retinas. Small quantities of (3S, 3'S)-zeaxanthin were also found in the adult retina, particularly in the macula. It is proposed that lutein and zeaxanthin are transported into an individual's retina in the same proportions found in his or her blood serum. Some of the lutein is then converted into meso-zeaxanthin, primarily in the macula, by a mechanism which is less developed in infants than adults.