An in vivo selection system for isolating targets of DNA binding proteins in yeast was developed and used to identify the DNA binding site for the NGFI-B protein, a member of the steroid-thyroid hormone receptor superfamily. The feasibility of the technique was verified by selecting DNA fragments that contained binding sites for GCN4, a well-characterized yeast transcriptional activator. The DNA binding domain of NGFI-B, expressed as part of a LexA-NGFI-B-GAL4 chimeric activator, was then used to isolate a rat genomic DNA fragment that contained an NGFI-B binding site. The NGFI-B response element (NBRE) is similar to but functionaily distinct from elements recognized by the estrogen and thyroid hormone receptors and the hormone receptor-like proteins COUP-TF, CF1, and H-2RIIBP. Cotransfection experiments in mammalian cells demonstrated that NGFI-B can activate transcription from the NBRE with or without its putative ligand binding domain.