Structural modifications have been performed on the selective a-amino phosphonic acid NEP inhibitor CGS 24592, to achieve dual ACE/NEP inhibition in vitro. (S)-N-Phosphonomethyl-valyl-(S)-(4-phenyl)phenylalanine (19) is representative of a new type of phosphorus-containing ACE/NEP inhibitors, approaching the in vitro potency of the sulfhydryl ACE inhibitor captopril and the NEP inhibitor thiorphan.