The Carotenoids Database currently provides information on 1167 natural carotenoids with 692 source organisms. Data on their structures and source organisms were obtained from the latest available original papers. The original chemical fingerprints newly investigated and described here make it easy to classify chemical modification patterns in carotenoid structures, to similarity search, and to predict some of the biological functions of carotenoids such as provitamin A, membrane stabilizers, odorous substances, allelochemicals, antiproliferative activity against cancer cells (new!), and reverse MDR activity (new!) at the present time. Our goal is to understand how organisms are related via carotenoids, either evolutionarily or symbiotically or in food chains through natural histories.