We have examined the NF-kappa B binding and functional activities in two stellate cell lines derived from normal (NFSC) and cirrhotic (CFSC) rat liver. Gel mobility shift assays revealed two bands in NFSC nuclear extracts that correspond to p65/p50 heterodimers and p50/p50 homodimers. In contrast, a single and more intense band that migrates faster was detected in CFSC nuclear extracts. This band supershifts with either p65 or p50 antibody. The differential NF-kappa B binding observed in these two cell lines appears to depend on the phosphorylation of the p65 subunit rather than the expression levels of either p65 or p50. The nonphosphorylated NF-kappa B form, present in CFSC cells, possesses significantly lower transcriptional activity compared to phosphorylated NF-kappa B, found in NFSC cells. To our knowledge, this is the first report on the NF-kappa B regulation at the p65 protein in hepatic stellate cells. It is likely that this regulation affects IL-6 expression and may represent a mechanism regulating hepatocyte death during fibrogenesis.