In 10 patients with end stage renal disease on regular haemodialysis the plasma concentrations and dialyzer clearance of isosorbide dinitrate (ISDN) were determined after an oral dose of a retarded release formulation of 60 mg ISDN. The maximal plasma concentration of ISDN 2-7 h after oral administration was higher (14 ng/ml) than has been reported in healthy volunteers. The haemodialyzer clearance of ISDN was 92.4 ml/min at a blood flow of 200 ml/min and dialysate flow of 500 ml/min. During a 5-h haemodialysis an average of 0.3 mg ISDN was removed from the patient's circulation, representing about 0.5% of the administered dose and about 3% of the available drug in the circulation. No influence of haemodialysis on the plasma level of ISDN was found.