Recently, Kosters et al. reported that Abcg5/Abcg8 mRNA expression in a variety of different mouse strains correlated with biliary cholesterol secretion rates [30]. In their studies, although diosgenin-fed mice showed a marked increase in biliary cholesterol output, mRNA levels of Abcg5 and Abcg8 were not altered. Using Western blot analyses, the protein level of Abcg5 was also not altered by diosgenin, although Abcg8 was not measured. They concluded that a parallel route for biliary cholesterol secretion might be operational, independent of the sterolins. While biliary cholesterol secretion is not completely absent in the Abcg8-deficient mice it would appear that sterolin-2 plays a major role in this process. In a genetic screen of plasma plant sterol levels, Sehayek et al. identified three loci that may be responsible for controlling plasma plant sterol levels and not one of these loci mapped to the murine STSL region [43]. Thus, there is support for at least four loci that may be involved in regulating plasma plant sterol levels. To date the STSL locus is the only one proven to be involved in dietary sterol trafficking and the identity of the others remains to be elucidated.