High density lipoprotein (HDL) participates in reverse cholesterol transport and in the delivery of cholesterol to steroid-producing tissues. Scavenger receptor class B type I (SR-BI) was recently shown to bind HDL and mediate internalization of its cholesterol content. We have cloned the rat homolog of this receptor, determined its chromosomal location, and examined its expression in rat tissues and in a model of follicular development, ovulation, and luteinization. The predicted protein contained two transmembrane domains, a leucine zipper motif, and a peroxisomal targeting sequence. The rat and human SR-BI genes were mapped to a region previously linked between rat and human chromosomes 12. SR-BI gene expression was detected in several rat tissues, with high levels in ovarian tissue, liver, and adrenal cortex, as determined by ribonuclease protection assay and in situ hybridization. A significant increase in SR-BI gene expression was detected in the late phase of corpus luteum formation, and transcripts were abundant in corpus luteum and in thecal cells at all stages of follicular development. In conclusion, the rat SR-BI complementary DNA predicted a protein with several conserved motifs, including a putative leucine zipper and a peroxisomal targeting sequence. The chromosomal locations of the rat and human SR-BI homologs suggest that this gene is a new member of a previously reported, conserved synteny group. SR-BI gene expression was high in steroid-producing tissues and in the liver, consistent with a role of this receptor in the uptake of HDL cholesterol.