We have previously generated a transgenic mouse line (EGF/Tag) in which simian virus 40 (SV40) T-antigen expression is directed by the mouse epidermal growth factor (EGF) gene promoter. In these mice, cellular hyperproliferation is observed in the submaxillary gland associated with SV40 T-antigen expression. In addition, SV40 T-antigen-expressing tumours of prostatic origin are seen. We have now derived immortalized cell lines from these tissues and have used the cells to perform a functional analysis of the EGF gene promoter. Cells were transfected with EGF promoter/reporter constructs, and an element located between 51 and 35 bases upstream of the EGF mRNA start site required for basal activity of the promoter was identified. Electrophoretic mobility-shift analysis suggests that three proteins bind to this region, one of which is either Sp1 or a closely related protein.