A series of renin inhibitors with novel modifications at the P2 site has been prepared. Structure-activity relationships reveal that for a particular P2 fragment the in vitro potency is highly dependent on the nature of the P2' portion in addition to the P1-P1' group. The length of the P2 side chain and choice of epsilon-N P2 substitution have been found to be important for in vitro potency although the degree of unsaturation in the P2 side chain is not particularly significant. Molecular modeling studies have shown that it is possible for the P2 side chain to interact unfavorably with the P2' binding site. It has been possible to control the specificity for renin over cathepsin D by correct modification at the P2' and P1-P1' sites. Variations at the P4 site have been utilized to lower the log P values of these renin inhibitors while maintaining high potency. Compound 42, which exhibited an IC50 of 3.70 nM, log P of 2.3, and showed high specificity for renin, was selected for further studies. It was found to be very stable under neutral, acidic, and basic conditions. In simulated intestinal juice, compound 42 had a half-life of 37 min while it was virtually unaffected by simulated gastric juice after 4 h. Compound 42 produced a significant hypotensive response upon intravenous administration to the salt-depleted normotensive cynomolgus monkey.