Essential hypertension is associated with increased intrarenal resistance that may go undetected unless the fractional distribution of cardiac output to the kidney is measured. Several hypotensive drugs induce a transient reduction of renal blood flow and glomerular filtration rate due to the reduction in renal perfusion. This may represent an untoward effect especially in subjects already presenting a clinically relevant reduction of renal function. Loop diuretics, cardioselective and intrinsic sympathomimetic activity (ISA) beta-blockers, calcium entry-blockers, and angiotensin-converting enzyme (ACE) inhibitors either do not significantly reduce or even increase renal perfusion. This is one more reason for considering these agents as first choice drugs for the treatment of hypertension.