The specific objective of this application is to investigate the role of complement, polymorphonuclear cells (PMNs), and metabolites of arachidonic acid in phototoxicity. The long-term objective of this proposal is to achieve better approaches in the management of patients with porphyrin and psoralen-induced phototoxicity by getting more complete understanding of the pathophysiology. Three phototoxic substances will be used: protoporphyrin (elevated in erythropoietic protoporphyria), uroporphyrin (elevated in porphyria cutanea tarda), and 8-methoxypsoralen (used in psoralen and ultraviolet-A therapy: Puva). The specific aims are: 1. To investigate the effect of phototoxic agents, irradiation, complement, and PMNs on selected cells in the dermis, namely, endothelial cells and mast cells. These cells will be cultured or purified, and incubated with phototoxic agents, and/or complement, and/or PMNs, and exposed to radiation. Cell damage, as well as the following parameters will be measured: endothelial cells: generation of eicosanoids; and mast cells: release of preformed mediators, and generation of eicosanoids. 2. To study the in vivo effect of phototoxic agents and irradiation on the metabolism of arachidonic acid in the skin. Mice will be rendered phototoxic, the skin will be removed, dermal-epidermal separation will be performed, and the metabolism of eicosanoids will be assessed by measuring the conversation of 3H-arachidonic acid to its metabolites. Similar study will be performed on serial skin biopsy specimens obtained from patients receiving PUVA.