New phosphinylalkanoyl prolines which have the general formula ##STR1## wherein R.sub.1 is lower alkyl, phenyl or phenyl-lower alkyl; R.sub.2 is hydrogen, phenyl-lower alkyl or a metal ion; R.sub.3 is hydrogen or lower alkyl; R.sub.4 is hydrogen, lower alkyl, phenyl-lower alkyl or a metal ion; and N is 0 or 1, Are useful as hypotensive agents.