Representative of prostaglandin ethers that can serve as an in vivo source of physiologically active prostaglandins when administered for example intravenously at the rate of 0.1 to 1.0 ??g/min, calculated as freed prostaglandins are ethers such as 9??,11??,15(S)-tris(lower alkyl' lower alkoxy' methyloxy)-13-trans-prostenoic acid; 9??,11??,15(S)-tris(lower alkyl' lower alkoxy' methyloxy)-5-cis,13-