Progesterone (P), the natural hormone, binds to its specific receptors to induce specific progestational effects. In addition to this binding, P is able to interfere with the binding sites of other steroids. Therefore the natural hormone exhibits an anti-estrogenic activity, and anti-androgenic activity and also exerts anti-mineralocorticoid effects. For a long time progesterone could not be used in clinical applications because of a rapid liver inactivation after oral administration. An oral micronized preparation of progesterone is now available which produces adequate plasma and tissue levels of progesterone. The preparation reproduces the anti-estrogenic effect of the natural hormone on the endometrium at the dose of 200 mg daily. It also reproduces the anti-mineralocorticoid effect and has no androgenic action. No side effects have been reported as far as lipids profile, coagulation factors and blood pressure are concerned. Therefore oral micronized progesterone appears suitable for hormonal replacement therapy in various areas, essentially postmenopause therapy, premenstrual syndrome, correction of irregular cycles and pregnancy maintenance.