Analogues of the renin octapeptide substrate were synthesized in which replacement of the scissile dipeptide with (3S,4S)-4-amino-3-hydroxy-6-methylheptanoic acid (statine, Sta) transformed the substrate sequence into potent, transition-state analogue, competitive inhibitors of renin. Synthesis and incorporation of the cyclohexylalanyl analogue of Sta, (3S,4S)-4-amino-5-cyclohexyl-3-hydroxypentanoic acid (ACHPA), gave the most potent inhibitors of renin yet reported, including N-isovaleryl-L-histidyl-L-prolyl-L-phenylalanyl-L-histidyl-ACHPA-L -leucyl-L- phenylalanyl amide [Iva-His-Pro-Phe-His-ACHPA-Leu-Phe-NH2,3], with renin inhibitions of Ki = 1.6 X 10(-10) M (human kidney renin), IC50 = 1.7 X 10(-10)M (human plasma renin), IC50 = 1.9 X 10(-9)M (dog plasma renin), and IC50 = 2.1 X 10(-8) M (rat plasma renin). This inhibitor 3, containing ACHPA, was 55-76 times more potent vs. human renin than the comparable Sta-containing inhibitor 1 and 17 times more potent vs. dog renin than 1. Inhibitor 3 lowered blood pressure in sodium-deficient dogs, with in vivo potency 19 times that shown by 1, in close agreement with the relative in vitro potencies. Structure-activity results are presented that show the minimal N-terminus for these inhibitors. An ACHPA-containing pentapeptide, N-[(ethyloxy)carbonyl]-L-phenylalanyl-L- histidyl-ACHPA-L-leucyl-L-phenylalanyl amide [Etoc-Phe-His-ACHPA-Leu-Phe-NH2,8], retained subnanomolar inhibitory potency. Molecular modelling studies are described that suggested the design of ACHPA.