This study was designed to evaluate anti-Xa activity hourly during the first 3 h after a single intravenous bolus of 0.5 mg/kg enoxaparin in 30 patients with end-stage renal disease (ESRD) who underwent haemodialysis, and in 30 patients with normal or mildly reduced renal function who underwent coronary angiography for chest pain (non-ESRD group). Mean +/- SD haemodialysis time was 3.9 +/- 0.3 h in the ESRD group. Of 24 patients diagnosed with coronary artery disease in the non-ESRD group, 20 underwent percutaneous coronary intervention (PCI). A peak anti-Xa activity > 0.5 IU/ml 10 min after enoxaparin injection was obtained in 90% and 93% of the non-ESRD and ESRD patients, respectively. The percentages of patients with peak anti-Xa activity in the target range (0.5 - 1.5 IU/ml) were similar in the two groups (non-ESRD 80%, ESRD 93%). Adequate anti-Xa activity (> 0.5 IU/ml) lasted about 2 h in both groups. It is concluded that a single intravenous low-dose enoxaparin (0.5 mg/kg) bolus provides anti-Xa activity adequate for elective PCI within 2 h irrespective of whether or not the patient had ESRD.