Beside well-established clinical benefits, the current doses of oestrogens may induce clinical side-effects leading to non-compliance and loss of efficacy. During a normal menstrual cycle the incidence of any cyclic discomfort is consistently reported to be lowest during the mild-follicular phase when plasma E2 remains between 60 and 150 pg/ml. The incidence of pregnancy-like symptoms such as bloating, breast tenderness and mood swings tends to increase in mid-luteal phase when E2 increases upto 150 pg/ml. On the other hand incidence of asthenia, sleep disturbances, depressive mood, headaches and migraines increase during perimenstrual days when E2 drops to 40 pg/ml or below. Accordingly experimental and human studies in castrated animals and postmenopausal women suggest that plasma E2 around 100 pg/ml is optimal for treatment of hot flushes, prevention of bone loss and cardiovascular protection. Due to large interindividual variation in estrogen clearance rate, it is unlikely that any standardized unique dose of oral or non-oral formulations will reproduce the optimal levels in all postmenopausal users. Efforts for individual titration are mandatory to improve compliance and actual efficacy on a long term. Because older postmenopausal women tend to have a better clinical tolerance to low E2 levels, objective markers of efficacy should also be identified when the aim of HRT is the prevention of osteoporosis or vascular diseases. In addition clinical and metabolic side-effects related to added progestins can be substantially reduced by the use of lower dose inducing amenorrhea and by progesterone instead of synthetic steroids.