IκBγ is one member of a family of proteins that can inhibit the nuclear localization of nuclear factor-κB. However, the other specific functions of IκBγ are still poorly understood, and its effects on tumor metastasis have not yet been characterized. We examined the consequences of targeting IκBγ in melanoma cells using a hammerhead ribozyme. We developed stable transformant B16-F10 melanoma cell lines that express a ribozyme that targets mouse IκBγ (IκBγ-144-Rz). Tail-vein injection of B16-F10 cells that stably express IκBγ-144-Rz into mice resulted in a significant reduction of the metastatic potential of these cells. IκBγ-144-Rz-expressing B16 cells were shown to have increased transcriptional activity of nuclear factor-κB. We then showed that IκBγ-144-Rz-expressing cells demonstrated both reduced invasion and increased apoptosis, suggesting the existence of pathways through which IκBγ promotes melanoma metastasis. Using gene expression profiling, we identified a differentially expressed gene set that is regulated by the stable suppression of IκBγ that may participate in mediating its anti-metastatic effects; we also confirmed the altered expression levels of several of these genes by quantitative real time polymerase chain reaction. Plasmid-mediated expression of IκBγ-144-Rz produced a significant inhibition of the metastatic progression of B16-F10 cells to the lung and resulted in significant anti-invasive and pro-apoptotic effects on murine Lewis lung carcinoma cells. Our results suggest a novel role for IκBγ in promoting the metastatic progression of melanoma.