In recent years considerable attention has been devoted to chemical modification of the orally active progestational agent 17a-ethynyltestosterone2 in the hope of obtaining even more active compounds. Among the outstanding modifications leading to potentiated progestational activity have been replacement of the C-10 angular methyl group by hydrogen (17a-ethynyl-19-nortestosterone3 and 17a-ethynyl-A5 (lo)-estren-17@-ol-3- ...