Blood and urine levels of atenolol were measured in 12 subjects: 2 anephric and 10 with creatinine clearances ranging from 0-122 ml/min per/1.73 m2. In a single-dose study subjects were given atenolol 100 mg by mouth and blood and urine levels were measured during the subsequent 72 h. In a repeated-dose study 10 subjects were given atenolol 100 mg for 20 days, and blood and urine levels were measured before and for 72 h after the final dose on day 21. In the single-dose study the peak blood level occurred later and the 24 h plasma concentrations increased as creatinine clearance decreased. The range in peak blood level was 6-fold throughout this range of creatinine clearance. The blood atenolol half-life (t1/2) increased from .apprx. 6 h to > 100 h with progressive renal failure and there was a corresponding decrease in elimination rate constant and increase in area under the curve. In the repeated-dose study there was good correlation between predose blood level of atenolol and both logarithm creatinine clearance and serum creatinine and the elimination rate constant correlated with creatinine clearance and the logarithm of serum creatinine. In the single-dose study minimum heart rates were observed just after the peak atenolol level. Blood pressure response did not correlate closely with serum atenolol levels. Dosing recommendations are suggested for patients with renal failure to take account of the effects of renal function on atenolol kinetics.