SAR407899 is a potent and selective Rho kinase inhibitor with promising antihypertensive activity. SAR407899 potently inhibits endothelin-1-induced constriction of renal resistance arteries. SAR407899 is equipotent against human and rat-derived Rho-kinase 2 with inhibition constant values of 36 nM and 41 nM, respectively. SAR407899 is approximately 8-fold more active than fasudil. SAR407899 potently (mean IC(50) values: 122 to 280 nM) and species-independently relaxed precontracted isolated arteries of different species and different vascular beds. The antihypertensive effect of SAR407899 was superior to that of fasudil and Y-27632.