The African-American Study of Kidney Disease and Hypertension pilot study randomized 94 nondiabetic black men and women (mean age, 53 years; 75% male) with presumed hypertensive nephrosclerosis and a baseline glomerular filtration rate (GFR) of 25 to 70 mL/min/1.73 m2 (mean, 52.3 mL/min/1.73 m2) to blood pressure control at either a low mean arterial pressure (MAP) goal of < or = 92 mm Hg or a usual MAP goal of 102 to 107 mm Hg and an antihypertensive drug regimen that included either a calcium antagonist (amlodipine), a beta-blocker (atenolol), or an angiotensin-converting enzyme (ACE) inhibitor (enalapril). After 3 months of follow-up (n = 90), the mean GFR was similar (53.0 mL/min/1.73 m2 v 53.7 mL/min/1.73 m2) to the baseline levels in participants randomized to the low MAP group (n = 44), whereas the mean GFR increased by 3.9 mL/min/1.73 m2 (P = 0.02) in participants randomized to the usual MAP group (n = 46). During the same period of time, the mean GFR increased significantly in participants randomized to the calcium channel blocker regimen (n = 28) (5.7 mL/min/ 1.73 m2; P = 0.01) but not in participants randomized to the beta-blocker regimen (n = 31) (1.7 mL/min/1.73 m2; P = 0.10) or the ACE inhibitor regimen (n = 31) (1.1 mL/min/1.73 m2; P = 0.52). Changes in GFR at 3 months were significantly different among the three treatment groups (P = 0.04). We conclude that the magnitude of short-term effects of blood pressure control and antihypertensive drug regimens on GFR should be considered when estimating sample size for clinical trials designed to evaluate the effects of these interventions on long-term changes in GFR slope.