Renin, a highly specific aspartyl protease, cleaves angiotensinogen, to yield angiotensin I, which is further converted into angiotensin II by ACE (Angiotensin Converting Enzyme). Angiotensin II constricts blood vessels leading to increased blood pressure. Discovery of new renin inhibitors for treatment of hypertension is a promising area of research. The SensoLyte® 520 Rat Renin Assay Kit provides a convenient assay for high throughput screening of renin inhibitors and for continuous assay of renin activity using a 5-FAM/QXL^®520 fluorescence resonance energy transfer (FRET) peptide. In the FRET peptide the fluorescence of 5-FAM is quenched by QXL^®520. Upon cleavage into two separate fragments by renin, the fluorescence of 5-FAM is recovered, and can be monitored at excitation/emission = 490/520 nm. The kit contains: 5-FAM/QXL^®520-based FRET rat renin substrate (Ex/Em=490/520 nm upon cleavage), assay buffer, rat recombinant renin, inhibitor, fluorescence reference standard for calibration, and an optimized assay protocol. Assays are performed in a convenient 96-well format.