Natural oestrogenic hormones are the appropriate substances for the therapy of climacteric complaints. After oral or parenteral administration, oestradiol valerate, the synthesis compound contained in various commercially available preparations, is completely converted into the natural substances 17 beta-oestradiol and valeric acid. The 17 beta-oestradiol produced on cleavage of the ester behaves in the organism like the endogenous steroid hormone. Oestradiol valerate and 17 beta-oestradiol are virtually dose-equivalent. No differences in the spectrum of action of the oestrogen and its ester have been found either in animal experiments or man. The pharmacokinetic behaviour and the biotransformation of the 17 beta-oestradiol originating from oestradiol valerate are no different from those of natural 17 beta-oestradiol. Differences of practical significance exist in respect of the quantitative effect of oestradiol valerate following oral and intramuscular administration, whereas 4 mg oestradiol valerate administered intramuscularly is therapeutically sufficient for a period of 2-4 wk (depot effect). As much as 2 mg daily over 3 wk must be administered via the oral route to achieve the same effect. This difference is due to the greatly diverging pharmacokinetic behaviour of oestradiol valerate depending on which of the two modes of administration is employed.