Using 42 nucleotide sequences extracted from the Transcription Regulatory Regions Database (TRRD) containing SF-1 transcription factor binding site, we have determined the decanucleotide (GTCAAGGTCA) consensus sequence for SF-1 binding. In the frequency matrix of this sequence nucleotides between the 3rd and the 7th position had the highest frequency and guanine nucleotides at the 6th and the 7th positions were recognized in all nucleotide sequences. The latter suggests a crucial role of these guanines for the interaction of DNA with SF-1 protein. The determined consensus and frequency matrix were used for search of putative SF-1 binding sites in regulatory regions of two genes, encoding mouse Cyp17 (17alpha-hydroxylase/17-20-lyase) and 3betaHSDI (3beta-hydroxysteroid dehydrogenase/4delta-5delta-isomerase I), the microsomal enzymes involved in steroidogenesis. 5;-Flanking regions of genes encoding Cyp17 and 3betaHSDI were shown to contain six and five such binding sites, respectively. The presence of the putative SF-1 binding sites in the regulatory regions of mouse Cyp17 and 3betaHSDI suggests that gene SF-1 could represent one of the putative genes which (as we predicted earlier) determine coordinated inheritable variability of hormonal activity in mouse Leydig cells.