The aim of this study was to evaluate the effectiveness of captopril for the prevention of the increase of arterial pressure during orthopaedic surgery requiring the application of lower limb tourniquets with balanced anaesthesia. Twenty consecutive patients were included in the study and were randomly divided into two groups. The first (n = 10) received 50 mg captopril orally together with the preanaesthetic medication, the second (n = 10) received a placebo at the same time. The different variables studied (arterial pressure, heart rate) were continuously measured. This study demonstrated that the pretreatment with captopril did not prevent an increase of the arterial pressure during the application of a tourniquet. The means of the systolic and diastolic arterial pressures at the end of the application of the tourniquet were 128/86 and 128/81 in the captopril group and the placebo group, respectively. This result shows that the renin-angiotensin system does not significantly contribute to the increase of the arterial pressure induced by a tourniquet.