Updated project metadata. This proteomic study This proteomic study focuses on the role of reversible thiol oxidation after hexyl aminolevulinate mediated PDT (HAL-PDT). The human epidermoid carcinoma cell line A431 was used as model system and red light as light source, a clinical relevant in vitro model. The light dose dependent cell cytotoxicity was measured by resazurin assay. The most clinical relevant dose, LD100, was used for the proteomic part of the study and cells where harvested 30 min after treatment. The reversibly oxidized thiol proteins were selected by biotinylation and identified by mass spectrometry. This proteomic technique revealed over 1100 thiol proteins which were reversibly oxidized after HAL-PDT. Identified proteins were analysed by bioinformatics (IPA and GO) and a list of reliable identified proteins (282 proteins) where further analysed. Both the cellular location and function was determined for these proteins. In addition, 18 of the proteins where identified as redox regulated, 36 to be a part of the apoptotic pathway and 9 to be both redox regulated and a part of apoptotic pathway. From these results we suggest redox regulated proteins as a trigger mechanism for PDT induced apoptosis.focuses on the role of reversible thiol oxidation after hexyl aminolevulinate mediated PDT (HAL-PDT). The human epidermoid carcinoma cell line A431 was used as model system and red light as light source, a clinical relevant in vitro model. The light dose dependent cell cytotoxicity was measured by resazurin assay. The most clinical relevant dose, LD100, was used for the proteomic part of the study and cells where harvested 30 min after treatment. The reversibly oxidized thiol proteins were selected by biotinylation and identified by mass spectrometry. This proteomic technique revealed over 1100 thiol proteins which were reversibly oxidized after HAL-PDT. Identified proteins were analysed by bioinformatics (IPA and GO) and a list of reliable identified proteins (282 proteins) where further analysed. Both the cellular location and function was determined for these proteins. In addition, 18 of the proteins where identified as redox regulated, 36 to be a part of the apoptotic pathway and 9 to be both redox regulated and a part of apoptotic pathway. From these results we suggest redox regulated proteins as a trigger mechanism for PDT induced apoptosis.