The two putative promoter regions of the human insulin-like growth factor-I (IGF-I) gene, located upstream of the two alternatively used leader exons 1 and 2, were tested for promoter activity in transient transfection assays. Both regions were shown to possess promoter activity. The results further indicate cell-type-specific regulation of the activities of the two promoters in endogenously IGF-I producing human cell lines of different origin.