In this work, 15 prodrugs of 17β-estradiol have been synthesized and characterized, and the kinetic profile of the compounds has been studied in rats, pigs and dogs after oral administration. All 15 substances were investigated in the rat model. The five substances, showing the highest bioavailability in this model, were selected for studies in pigs, and the two most promising compounds in pigs were subsequently tested in dogs.In the rat model, an improvement of the oral bioavailability with a factor three or more was seen from six of the prodrugs. In the pig model, a bioavailability, 2.5-3.7 times higher than that of estradiol was seen from three of five prodrugs.The dog model appeared extremely sensitive in proving the prodrug effect. Compared with the parent compound, an improved bioavailability of approximately 30 times was observed from the two prodrugs tested. After administration of these substances, the ratio of estrone and estradiol in serum was 0.4-0.6. It can be concluded that in all three animal species, the most promising prodrug properties appeared from the 3-glutarate-17-succinate and 3-benzyl-succinate esters of estradiol.