Subarachnoid hemorrhage (SAH) initiates a series of cellular and molecular events, some of which involve a mitogen activated protein kinase, c-jun N-terminal kinase (JNK). However, precise details regarding activation of c-jun in the vessel wall after SAH largely remain to be elucidated. In this study, we therefore investigated the localization and time-dependent expression of c-jun in the rat basilar artery after SAH in a rat single-hemorrhage model featuring infusion of autologous arterial blood. Basilar arteries were obtained at 2, 6 and 12h and 1, 2, 4 and 7 days after SAH, as well as from controls. Western blot analysis with c-jun, phosphorylated c-jun at Ser(63), and actin antibodies revealed that c-jun was immediately phosphorylated at Ser(63) within 2h, thereafter gradually becoming dephosphorylated, while total c-jun and actin levels remained almost unchanged. Immunohistochemistry demonstrated phosphorylation of c-jun at Ser(63) to occur in smooth muscle cells of the basilar artery 2h after SAH. These results indicate that c-jun is activated in the basilar artery immediately after the onset of SAH, presumably resulting in transcription of immediate early genes and smooth muscle cell proliferation.