Abstract: Compositions and methods relating to the regulation of transport of cholesterol into the mitochondria of a cell and, therefore, for the regulation of steroidogenesis are provided. Compositions include nucleic acid molecules encoding a steroidogenic acute regulatory protein (StAR), StAR protein molecules and peptides having amino acid sequences as disclosed herein, and anti-StAR antibodies. Methods include immunoassays using anti-StAR antibodies and nucleic acid based screening methods for pathologies correlated with defects in StAR, such as lipoid congenital adrenal hyperplasia and dose sensitive sex reversal. In addition, these compositions and methods may be useful for treatment of steroid hormone-dependent disorders, in particular, for lipoid congenital adrenal hyperplasia.