Treatment of hypertension with ACE inhibitors in diabetic patients reduces proteinuria and slows progression of nephropathy compared with agents that do not maintain declines in proteinuria. Calcium channel blockers (CCBs) have variable effects on proteinuria; their long-term effects on progression of diabetic nephropathy are not known. The current study examines the hypothesis that CCBs that maintain reductions in proteinuria slow progression of nephropathy associated with non-insulin dependent diabetes mellitus (NIDDM) by a degree comparable to ACE inhibitors, given similar levels of blood pressure control. To test this hypothesis we randomized 52 patients with NIDDM associated nephropathy and hypertension, mean age of 63 +/- 8 years, to either the ACE inhibitor, lisinopril (N = 18), nondihydropyridine CCBs (NDCCBs), verapamil SR (N = 8) or diltiazem SR (N = 10), or the beta blocker, atenolol (N = 16). Goal blood pressure was < or = 140/90 mm Hg. Patients were followed for a mean period of 63 +/- 7 months. The primary end point was change in creatinine clearance (CCr) slope in each group. There was no significant difference in mean arterial pressure reduction among the groups over the study period (P = 0.14). The mean rate of decline in CCr was greatest in the atenolol group (-3.48 ml/min/year/1.73 m2; P < 0.0001). There was no difference in the CCr slopes between lisinopril and NDCCBs groups (P = 0.36). Proteinuria was reduced to a similar extent in the lisinopril and NDCCBs groups (P > 0.99). Therefore, in persons with renal insufficiency secondary to NIDDM, similar levels of blood pressure control with either lisinopril or NDCCBs slowed progression of renal disease to a greater extent than atenolol. Moreover, this enhanced slowing of renal disease progression correlated with sustained and significant reductions in proteinuria, findings not observed in the atenolol group.