Recombinant plasmids specific for bovine adrenocortical cytochromes P-450scc and P-45011 beta have been identified and characterized. Using these cDNA inserts as probes, it is found that tissue specificity of gene expression for these two proteins is as expected. Cytochrome P-450scc mRNA is found in adrenocortical and corpus luteum RNA while cytochrome P-45011 beta mRNA is found only in adrenocortical RNA. Neither mRNA was detected in heart, liver or kidney RNA. Cytochrome P-450scc mRNA is found to be 1.9 kb in length while cytochrome P-45011 beta mRNA is found to be 4 kb in length. Treatment of bovine adrenocortical cells with ACTH or other modulators results in increased levels of cytochrome P-450scc and cytochrome P-45011 beta mRNAs. Cytochrome P-450scc is found to be encoded by a limited number or even a single gene.