Steroid hormones, the lipophilic molecules, are synthesized from cholesterol which in turn is formed from acetate. Plasma low-density lipoproteins derived from diet contribute to the major part of cholesterol. Cholesterol produced in the liver circulates in the form of high-density lipoprotein and low-density lipoprotein. Major sites of steroid synthesis include the adrenals, testes, ovaries, and placenta. The four major types of steroid hormones are progestins, androgens, estrogens, and corticoids, which contain 21, 19, 18, and 21 carbons, respectively. Steroid hormones are synthesized by dehydrogenases and cytochrome P450 enzymes from cholestane, a common cholesterol precursor through hydroxylation and dehydroxylation-oxidation reactions. Pregnenolone metabolism through the delta 5 pathway in the human ovary serves as the only route for estradiol synthesis. The most potent endogenous androgen is DHT and is predominantly seen in epididymis and prostate.