Estrogen replacement therapy is effective in relieving typical postmenopausal symptoms; it prevents osteoporosis and reduces the risk of cardiovascular diseases. Various delivery forms and routes of administration of estradiol are currently available, but transdermal delivery is getting increasingly popular. It bypasses the hepatic first-pass metabolism, eliminates poor absorption during gastrointestinal disturbances, minimizes the potential of drug interactions and allows delivery of constant levels ofhormones. Transdermal delivery systems (TDS) enable fast hormone release in blood circulation. There are two different TDS - the transdermal reservoir patch and matrix patch. The transdermal matrix system may be preferable because its use is associated with a lower incidence of side effects, more stabile plasma estrogen concentrations, delivery of consistent therapeutic serum levels of estradiol and better bioavailability. Results obtained by comparing several matrix systems show that different TDS with the same declared amount of hormones released in bio od circulation do not have equal bioavailability and pharmacokinetic profile. Comparison is made of absorption and bioavailability of estradiol between TDS and different therapeutic forms, i.e. gel. Pharmacokinetic profiles of estradiol are different, but bioavailability and Cmax do not differ significantly. There is a big difference in cmin (lower for TDS). Fluctuations in plasma concentrations are therefore higher for TDS. TDS is also used as a contraceptive. Dosing schedule is simple to follow, user-controlled, and easily reversed. Comparison is made between 3 contraceptive methods: combined oral contraceptive, TDS and vagina! ring. Individua! serum levels with combined oral contraceptive showed the highest variability as a result of its dosing regimen and exposure to ethinylestradiol was the highest. Vaginal administration ofhormones affords much lower, more stable and far more precise dosing than either the transdermal or oral routes.