A clone bearing the rat CYP17 gene has been isolated and the sequence determined for 417 nucleotides 5' to the translation start site. The sequence shows one difference, a G-C inversion, with that published by Zhang et al. (1992). A transcription initiation site has been located at position -41 relative to the translation start site; this confirms the location published by Nason et al. (1992) with the caveat of the G-C inversion, so that the transcription start site becomes G instead of C. Overall percent similarities of this sequence with those of bovine, human, pig and mouse show values of 58, 64, 65, and 82, respectively. Similar comparisons done for the cAMP-responsive sequences, CRS-1 and CRS-2 (Lund et al., 1990), show 42, 55, 47 and 95% similarities for CRS-1, and 56, 77, 71 and 90% for CRS-2. These comparisons suggest that the highly conserved rat and mouse gene sequences corresponding to the bovine CRS-1 and CRS-2 may be important for either negative regulation of this gene in the adrenal or positive regulation in the gonads of these two species.