Apoptosis Signal-regulating Kinase 1 (ASK1) is known to either induce apoptosis or differentiation in various cell lines of neuronal origin. We analyzed the effect of the constitutively active mutant of ASK1 (ASK1-Delta N) in an adenoviral vector in four neuroblastoma cell lines, two murine, C1300 and NXS2, and two human, SH-SY5Y and IMR-32. Already after 24 h upon infection, C1300 and SH-SY5Y cells arrested in growth when judged by [(3)H]thymidine incorporation, and the majority of the cells demonstrated apoptotic appearance, which was confirmed by DNA-laddering in gel electrophoresis. In contrast, NXS2 and IMR-32 cell lines remained unaffected. Immunoblotting revealed strongly phosphorylated p38 MAPK accompanied by weakly phosphorylated JNK in C1300 and SH-SY5Y, whereas none of these kinases were activated by adenoviruses expressing the kinase negative ASK1 mutant or beta-galactosidase. There was no expression of phosphorylated kinases in IMR-32 cells, but NXS2 showed a faint band of phosphorylated p38 MAPK. Addition of the p38 MAPK specific inhibitor, SB203580, protected C1300 and SH-SY5Y cells from apoptosis induced by ASK1-Delta N. The anti-neoplastic agent, paclitaxel, activates ASK1 and JNK, and promotes the in vitro assembly of stable microtubules. Addition of 10 nM paclitaxel sensitised the NXS2 cell line to ASK1-induced cell death. Our results indicate that ASK1 induces apoptosis in neuroblastoma cells mainly via the p38 MAPK pathway, and resistant neuroblastoma cells can be sensitised to ASK1 by paclitaxel.