The renal effects of oral maintenance doses of nicardipine 60-120 mg/day have been studied in 18 hypertensive patients with Type 2 (non-insulin-dependent) diabetes mellitus: 6 with normoalbuminuria (urinary albumin excretion rate, AER less than 20 micrograms.min-1, Group A); 6 with incipient nephropathy, (AER 20-200 micrograms.min-1, Group B); and 6 with overt nephropathy (AER greater than 200 micrograms.min-1, Group C). Treatment for 4 weeks significantly lowered the systolic and diastolic blood pressures and reduced total renal vascular resistance in all three groups. Nicardipine increased renal blood flow significantly in Group C and slightly in Group B, and had no effect in Group A. Glomerular filtration rate remained unchanged in all three groups. It significantly reduced AER and the fractional clearance of albumin in Group B, whereas AER in Groups A and C was not altered. Plasma renin activity, aldosterone concentration, osmotic pressure, serum total protein and albumin concentrations and haemoglobin A1c level were similar in the control and nicardipine phases in all three groups. The results suggest that nicardipine may preserve renal function whilst having a concomitant hypotensive action in hypertensive Type 2 diabetic patients with normoalbuminuria and incipient nephropathy, and that the drug may improve renal blood flow in patients with overt nephropathy. The effect of the drug on urinary albumin excretion may deserve further investigation.