alpha(1)-Antitrypsin (AAT) is the major serine proteinase inhibitor (SERPIN A1) in human plasma. Its target proteinase is neutrophil elastase and its main physiological function is protection of the lower respiratory tract from the destructive effects of neutrophil elastase during an inflammatory response. Circulating levels of AAT rise 2-3-fold during inflammation and the liver produces most of this increase. The cytokines oncostatin M (OSM) and interleukin-6 have been shown to be mainly responsible for this effect, which is mediated via the interaction of cytokine-inducible transcription factors with regulatory elements within the gene. In the present study, we report for the first time that OSM stimulation of hepatocyte AAT occurs via an interaction between the hepatocyte promoter and an OSM-responsive element at the 3'-end of the AAT gene. This effect is mediated by the transcription factor signal transducer and activator of transcription 3 ('STAT 3') binding to an OSM-responsive element (sequence TTCTCTTAA), and this site is distinct from, but close to, a previously reported interleukin-6-responsive element.