Several lines of evidence suggest that the growth factor insulin-like growth factor-II (IGF-II) is involved in the genesis of several types of tumors and may have autocrine effects on tumor progression when overexpressed. The human IGF-II gene is a complex transcription unit. Multiple transcripts are synthesized as a result of alternate promoter usage and the splicing of unique 5'-untranslated regions to common coding exons. We have examined two human tumor cell lines that both produce IGF-II protein which can function as an autocrine growth factor. Interestingly, each cell line uses a different IGF-II promoter; Hep3B cells predominantly activate P3, whereas in SW613 cells P4 is the preferred promoter. Here, we examine the differential transcriptional activation of the human IGF-II gene in Hep3B and SW613 cells by means of transient transfection assays and electrophoretic mobility shift analysis. The results indicate that production of IGF-II protein is mainly regulated at the level of transcription. Additional regulation takes place at the levels of messenger RNA stability and efficiency of translation.