This gene encodes a member of the cytochrome P450 superfamily of enzymes. The cytochrome P450 proteins are monooxygenases which catalyze many reactions involved in drug metabolism and synthesis of cholesterol, steroids and other lipids. This endoplasmic reticulum protein is involved in the conversion of cholesterol to bile acids. Its substrates include the oxysterols 25-hydroxycholesterol, 27-hydroxycholesterol and 24-hydroxycholesterol. Alternate splicing results in multiple transcript variants.