Clorazepate dipotassium (Tranxilium) is one of the benzodiazepines which is widely used for oral premedication. After oral administration it is decarboxylated to its active metabolite nordiazepam (desmethyldiazepam). Nordiazepam is also commercially available in the form of drops (Tranxilium N). The aim of the present study was to compare the effect of these drugs on preoperative anxiety. One hundred and eight patients scheduled for orthopaedic surgery (ASA I-II) were studied. Medication was administered at 10 p.m. the evening before surgery (E) and at 7 a.m. on the morning of surgery (M). There were four groups: 1) E no medication; M clorazepate dipotassium; 2) E no medication; M nordiazepam; 3) E clorazepate dipotassium; M clorazepate dipotassium, 4) E clorazepate dipotassium; M nordiazepam. Dosages were: clorazepate dipotassium: body weight < 55 kg: 10 mg; body weight > 55 kg: 20 mg; nordiazepam: 1 gtt/kg; 5 mg = 24 gtt). Anxiety was measured by using the self-evaluating Erlangen anxiety scales, which measure both background and situational anxiety. Background anxiety (EAS-H) was evaluated during the evening before surgery; situational anxiety (EAS-S) was evaluated at the same time and also on the day of surgery before premedication and immediately before surgery. Pulse rate was measured each time the test was administered. There were no differences between the groups in sex, age, weight or the intervals between premedication and anaesthesia induction (p > 0.05). There were no statistically significant differences between the groups with respect to background anxiety. Situational anxiety did not significantly increase or decrease at any of the testing times, nor were there any differences between the groups (p > 0.05). Heart rate did not vary between the groups or with time (p > 0.05). In this group of patients undergoing elective orthopaedic procedures, clorazepate prevented a rise in anxiety in the immediate preoperative period. Since clorazepate is rapidly metabolized to nordiazepam when administered orally it might be predicted that the two drugs have similar properties. This hypothesis is confirmed by the results of the present study. We conclude that orally administered clorazepate dipotassium and nordiazepam have a similar effect on preoperative anxiety.