The insulin gene is expressed almost exclusively in the β cells of the islets of Langerhans, where transcriptional control is conferred by cis-acting regulatory sequences located within 300400 base pairs from the transcription start site. These elements bind β-cell restricted (e.g. PDX-1) and ubiquitous (E47) transcription factors. In non-β cells the insulin gene is localised within tightly packed (hetero) chromatin structures. Developments in understanding the role of chromatin and protein-DNA interactions in the control of gene expression have led to a technology based on designer transcription factors that regulate specific genes in vivo. These proteins contain two modules: a zinc finger based DNA binding domain and a functional domain which can either activate or repress genes. Such engineered zinc finger transcription factors (ZFP-TFs) have been used to regulate a variety of clinically relevant genes in human cells, including erythropoietin and VEGF. Here we describe an engineered zinc finger transcription factor (ZFP) that was isolated from a library of ZFPs on the basis of its ability to strongly activate the endogenous insulin gene in HEK-293 cells. Under similar conditions a PDX-VP64 construct that has been shown by others to activate the endogenous insulin gene in liver had no effect. The INS-ZFP contains a 3-finger DNA-binding domain, the nuclear translocation signal from SV40 large T antigen, the transactivation domain of the VP16 protein from Herpes simplex, and a Flag tag. The INS-ZFP acts directly on the insulin promoter through sequences located within the proximal promoter region. These sequences are absent from the rat insulin promoter.