The invention relates to the use of derivatives of E-type prostaglandins as EP.sub.2 agonists, in general, and, in particular as ocular hypotensives. The PGE derivatives used in accordance with the invention are represented by the following formula I: ##STR00001## wherein the hatched segment represents an .alpha. bonds, the solid triangle represents a .beta. bond, the wavy segments represent .alpha. or .beta. bond, dashed lines represent a double bond or a single bond, X is selected from the group consisting of hydrogen and halogen radicals, R.sup.3 is heteroaryl or a substituted heteroaryl radical, R.sup.1 and R.sup.2 are independently selected from the group consisting of hydrogen or a lower alkyl radical having up to six carbon atoms, or a lower acyl radical having up to six carbon atoms, R is selected from the group consisting of CO.sub.2R.sup.4, CONR.sup.4.sub.2, CH.sub.2OR.sup.4, CONR.sup.4SO.sub.2R.sup.4, P(O)(OR.sup.4) and ##STR00002## wherein R.sup.4 is selected from the group consisting of H, phenyl and lower alkyl having from one to six carbon atoms and n is 0 or an integer of from 1 to 4.