We have established that phaeomelanin is photolabile under biologically significant conditions. We believe that there are several mechanisms by which this observation could account for the increased sensitivity to ultraviolet light exhibited by people of Celtic ancestry. In order to test our hypotheses it is necessary to characterize the photodegradation products of phaeomelanin. To aid in this task we propose to undertake the synthesis and photolysis of several model compounds. The question of the detailed structure of phaeomelanin further complicates analysis of its photodegradation and we propose to reinvestigate the structure by a combination of chemical modifications and modern spectroscopic techniques. It is the primary goal of this proposal to isolate and characterize the photolysis products of phaeomelanin.