Evidence is presented that virus-induced transcriptional activation of the human interferon-beta gene is mediated by repeated sequence units each consisting of 6 bp. The repeated units are present in the region between -65 and -109 relative to the cap site. We chemically synthesized the "consensus" DNA sequence units and tested their ability to confer virus inducibility on cognate and noncognate promoters. Most of such sequence units when tandemly repeated indeed mediate virus-induced activation of the promoter sequences. The most efficient sequence unit, AAGTGA, contributes incrementally in virus-induced activation of transcription and manifests properties of an inducible enhancer. Evidence is also provided that suggests that interaction of a positive regulatory factor(s) with this regulatory region.