Oxycarotenoids, produced through the oxidation of carotenoids, play critical roles in plants. This reaction is mediated by a specific enzyme, ${eta}$-carotene hydroxylase, which adds hydroxyl groups to the ${eta}$-rings of carotenes. To investigate the effect of the ${eta}$-carotene hydroxylase gene (Chyb) on oxycarotenoid biosynthesis, we generated transgenic Arabidopsis plants that over-expressed Chyb under the control of a 355 promoter. Their levels of zeaxanthin and neoxanthin were two- to three-fold greater relative to the wr, while that of violaxanthin, a final product in the xanthophyll pathway, was 1.3-fold higher than the control. In contrast, the amount of ${eta}$-carotene declined as much as 2.4-fold, depending on the particular transgenic line. Interestingly, astaxanthin was produced in the transgenics, but not in the WT. These data suggest that, with the aid of unknown factors in the host, carotenoids could be converted into metabolites in the astaxanthin biosynthetic pathway. Microarray analysis was used to identify several genes that were consistently up-or down-regulated in transgenic chyB leaves compared with the controls. Here, we also discuss possible modifications in leaf carotenoids, and the importance of these data from a nutritional standpoint.