The pharmacokinetics of diltiazem were studied in seven patients with chronic renal failure (CRF) not requiring dialysis and in three healthy volunteers after a rapid i.v. infusion of 20 mg. Mean plasma concentrations at the end of infusion were 3.15 times higher in patients with CRF than in healthy volunteers. From 0.5 to 12 h post-infusion, the difference remained between 25 per cent and 73 per cent. Mean AUC0-infinity was statistically greater in patients than in volunteers while mean V area, CLtot, and CLren were statistically lower. The t1/2 alpha and t1/2 beta values were not significantly (p greater than 0.05) different between patients and volunteers. Renal excretion was statistically more important in volunteers (6.6 per cent of the dose) than in patients (1.2 per cent of the dose). We therefore conclude that CRF does not influence t1/2 beta of diltiazem but it interferes with the extent and possibly the rate of its extravascular distribution. That could result in transient high plasma concentrations after rapid i.v. infusion.