Renin, the rate-limiting enzyme in the formation of angiotensin II, is an aspartyl protease that is critical for the blood pressure regulation. Therefore, inhibiting renin may offer potential benefits for the treatment of hypertension. We describe a homogeneous, continuous FRET assay for evaluating renin inhibitors, based on an intramolecularly-quenched fluorogenic peptide terminally labeled with DNP and AMP. Cleavage of the internal Leu-Val bond provides a sensitive fluorescence signal, which requires only 200 picomolar renin, thereby enabling evaluation of inhibition reversibility rates by a dilution protocol. As gauged by the recovery of activity for pre-equilibrated renin-inhibitor samples relative to control reactions, a statine-based peptide renin inhibitor and a 3,4-disubstituted piperidine inhibitor were differentiated as very slowly reversible and rapidly reversible inhibitors of renin, respectively.