Tumor necrosis factor-alpha (TNF-alpha) is released from cells by proteolytic cleavage of a membrane-anchored precursor. The TNF-alpha-converting enzyme (TACE/ADAM17) is the major sheddase for ectodomain shedding of TNF-alpha. At present, however, it is poorly understood how its catalytic activity is regulated. Here, we show that nardilysin (N-arginine dibasic convertase; NRDc) enhanced TNF-alpha shedding. In a cell-based shedding assay, expression of NRDc synergistically enhanced TACE-induced TNF-alpha shedding. A peptide cleavage assay in vitro showed that recombinant NRDc enhances the cleavage of TNF-alpha induced by TACE. Notably, co-incubation of NRDc completely reversed the inhibitory effect of a physiological concentration of salt on TACE's activity in vitro. Overexpression of NRDc in TACE-deficient fibroblasts resulted in an increase in the amount of TNF-alpha released. Co-expression of NRDc with ADAM10 promoted the release compared with the sole expression of ADAM10. These results suggested that NRDc enhances TNF-alpha shedding through activation of not only TACE but ADAM10. Our results indicate the involvement of NRDc in ectodomain shedding of TNF-alpha, which may be a novel target for anti-inflammatory therapies.