There exists a wealth of knowledge on cholesterol synthesis and metabolism. Research in this area has been awarded a number of Nobel prizes during the last five decades. Maintenance of cholesterolhomeostasis is very important from a clinical point of view, and disturbances in this homeostasis may have serious consequences. Research during the last decades has focused on the key enzymes involved in cholesterol synthesis and metabolism. Although there exists a lot of general knowledge regarding the mechanisms involved in this regulation, there are still several unclear points. The importance of oxysterolsis one of the uncertainties. Many oxysterols have a high potential to downregulate the rate-limiting enzyme in cholesterol synthesis, HMG-CoA reductase (for a general review, see ref 3). Since oxysterols are formed in biological systems by both enzymatic and nonen-zymatic mechanisms, it has been suggested that they may be important physiological regulators of choles-terol homeostasis. 4’5