The toxicology of benzo[a]pyrene (BaP) has been mainly studied with regard to the carcinogenicity of its metabolites, but its phototoxicity is not well understood. Although some studies have indicated the lethal phototoxicity of BaP, there have been no reports regarding the pattern of cell death induced by this agent. In this study, we investigated the pattern and mechanism of cell death induced by coexposure to BaP plus ultraviolet A (UVA) in Jurkat cells. Coexposure to BaP plus UVA showed dose-dependent cytotoxicity. The pattern of cell death was apoptotic as determined by cell shrinkage, chromatin condensation, appearance of subdiploid apoptotic nuclei and translocation of phosphatidylserine to the outer membrane leaflet. Coexposure also strongly increased caspase-3/7 activity and slightly elevated those of caspase-8/6 and -9. The pan caspase inhibitor Z-VAD-CH(2)-DCB partially inhibited the phototoxicity of BaP. Cytochrome c release was observed 6 h after coexposure, but not after 1 h. Furthermore, the phototoxicity was inhibited by NaN(3) (quencher of singlet oxygen), but not by mannitol (quencher of hydroxy radicals). Chromatin condensation and translocation of phosphatidylserine were also inhibited by NaN(3), suggesting that the induction of apoptosis by coexposure to BaP plus UVA was due to singlet oxygen production.