Prostaglandin cathartic

A process for providing a cathartic effect to a patient in need thereof which comprises administering to cathartic-inducing effective amount of a 15-keto-16-halogen PGA, PGE or PGF having the following skeleton:

• ##STR29## and wherein said skeleton is saturated or contains at least one unsaturated bond which is a 2,3-, 5-6- or 17,18- double bond or a 5,6- triple bond, and is not further substituted or is further substituted at at least one of C-3, C-6, C-17, C-19 and C-20 positions of the skeleton by a halogen atom, an alkyl group, an alkoxy group, a carbonyl group, a hydroxyl group, a phenyl group or a phenoxy group, or a pharmaceutically acceptable 1-ester or salt thereof, and a pharmaceutically acceptable carrier.