Nuclear factor kappa-B (NF-kappaB), extracellular regulated kinase (ERK 1/2) and c-jun-N terminal kinase (JNK) play an important role in testicular ischemia. We investigated the patterns of ERK1/2, JNK and p38 activation in NF-kappaB knockout (KO) mice subjected to testicular torsion. KO and normal littermate wild-type (WT) animals underwent at 1 h testicular ischemia followed by 24 h reperfusion (TI/R). Sham testicular ischemia-reperfusion mice served as controls. ERK 1/2, JNK and p38 expression by western blot analysis, tumor necrosis factor-alpha (TNF-alpha) expression (RT-PCR and western blot analysis) and a complete histological examination were carried out. TI/R caused a greater increase in phosphorylated form of ERK 1/2 in KO mice than in WT animals in either the ischemic testis and the contralateral one. By contrary, active form of JNK and p38 were completely abrogated in both testes of KO mice, while WT animals showed a significant activation of those kinases in both testes. TNF-alpha expression was markedly reduced in KO mice when compared to WT mice either at the mRNA and the protein level. Finally TI/R-induced histological damage was markedly reduced in KO mice. Our data indicate that NF-kappaB plays a pivotal role in the development of testicular ischemia-reperfusion injury and suggest that, in the absence of the transcriptional factor, the up-stream signal JNK and p38 may be abrogated while ERK 1/2 activity is enhanced.