Amantadine is useful for the prevention and treatment of influenza A and for the treatment of Parkinson's disease and drug-induced extrapyramidal disorders. We have compared the pharmacokinetics of amantadine in patients with impaired or negligible renal function to that in normal subjects. The half-life of elimination in subjects with normal renal function was 11.8 +/- 2.1 hours (range, 9.7 to 14.5 h). Eight patients with various degrees of renal insufficiency (creatinine clearance from 43.1 to 5.9 mL/min . 1.73 m2) had half-lives of elimination from 18.5 h to 33.8 days. We also studied 10 patients on thrice-weekly hemodialysis. Assuming complete bioavailability of the drug, less than 5% of the dose was removed by each 4-hour hemodialysis. The mean half-life of elimination during chronic hemodialysis was 8.3 days (range, 7.0 to 10.3). We present guidelines for use of amantadine in patients with impaired renal function, including those on maintenance hemodialysis.