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Ultraviolet A (UVA; 320–400 nm) radiation in human skin fibroblasts induces a pattern of mitogen‐activated protein kinase (MAPK) activation consisting of a rapid and transient induction of p38 and c‐Jun‐N‐terminal kinase (JNK) activity but not extracellular signal‐regulated kinases (ERK). UVA activation of p38 can be inhibited by the singlet oxygen (¹O₂) quenchers azide and imidazole, but not by the hydroxyl radical scavengers mannitol or dimethylsulfoxide, pointing to the involvement of ¹O₂. The same effect has been shown for JNK. Like UVA, ¹O₂ generated intracellularly upon photoexcitation of Rose Bengal activates p38 and JNK but not ERK. p38 and JNK activation was also elicited by chemiexcitation for the intracellular generation of ¹O₂ by the lipophilic 1,4‐endoperoxide of N,N′‐di(2,3‐dihydroxypropyl)‐1,4‐naphthalene dipropionamide. In contrast, extracellular generation of ¹O₂, by irradiation of …