Twenty-seven patients (15 diabetics and 12 non-diabetics) with normal to moderately reduced renal function underwent femoral angiography with a low-osmolar contrast agent, iohexol (Omnipaque), under perexaminatory hydration. Fourteen patients were randomised to pretreatment with oral felodipine extended release (Plendil) 10 mg and 13 patients to placebo 3-4 h before angiography. GFR measured with [51Cr] EDTA-clearance decreased 24 hours after the angiography in the felodipine group from GFR 52.5 +/- 18.6 (mean +/- SD) to 46.2 +/- 16.5 ml/min (p < 0.01) and in the placebo group from 70.6 +/- 18.6 to 62.6 +/- 26.4 ml/min (p < 0.01). Serum creatinine increased significantly in the felodipine group from 128 +/- 61 to 139 +/- 67 mumol/l (p < 0.05) but not in the placebo group (122 +/- 54 to 125 +/- 51 mumol/l (ns)). The values of serum creatinine returned to baseline levels 7 days after angiography. During hydration there was only a slight reduction of GFR after angiography with iohexol. Thus, felodipine had no major effect on GFR after iohexol but, as baseline GFR tended to be lower in the felodipine pre-treated patients, it might have had some renoprotective effect in patients with more advanced renal failure.