Of the many carotenoids found within human tissue, only the carotenoids within the human retina can be assessed noninvasively at present. Such assessment should eventually provide a more complete understanding of the functional role of retinal lutein (L) and zeaxanthin (Z) (termed macular pigment, MP) in human vision. The emerging data allow for some initial observations. For example, there appears to be wide variation (>factor of 10) in the concentration of MP. Although MP levels have been recorded from nondetectable to 1.20 OD (optical density), the "average" levels, relative to what is possible, appear low. This may be due in part to the low average dietary intake of L and Z in the typical U.S. diet. Nonetheless, individual differences in MP may also be influenced by nondietary factors such as genetics, demographics and lifestyle characteristics. Some evidence indicates that the MP carotenoids may protect the retina and lens, and could improve vision through some optical mechanisms. Consequently, efforts to determine typical MP levels and the factors that influence individual differences in MP density should be continued.