The Wilms tumor gene WT1 encodes a Cys2His2-type zinc finger protein that can bind DNA and function as a transcriptional regulator. The pathological spectrum of tumorigenesis and various developmental defects produced by different WT1 alterations suggests that WT1 controls a number of subsequent effector genes. To define the role of WT1 in these developmental processes it will be important to elucidate mechanisms that govern expression of WT1 itself. To facilitate mapping of the WT1 promoter region and 5' control elements we have determined the sequence upstream of the WT1 transcription unit. This includes the Wit-1 gene that is transcribed in the opposite direction.