INTRODUCTION: The aim of this study was to investigate the haemodynamic changes that follow the appearance of pruritus during vancomycin administration. METHODS: We studied 50 patients scheduled for coronary artery bypass surgery, and we compared data from patients who exhibited pruritus with those from patients who did not. After the monitoring devices had been positioned, vancomycin (15 mg/kg) was continuously infused at a constant rate over 30 min, before induction of anaesthesia. Haemodynamic profiles were recorded before vancomycin infusion (time point 1); at 15 (time point 2) and 30 min (time point 3) after the beginning of vancomycin infusion; and 15 min after vancomycin infusion had been stopped (time point 4). At each time arterial and mixed venous blood samples were drawn to calculate the shunt fraction (Qsp/Qt). RESULTS: In patients who exhibited pruritus (group A, n = 17) at time point 3 versus time point 1, systemic vascular resistance index (SVRI) and arterial oxygen tension (PaO2) decreased significantly; cardiac index (CI), stroke volume index (SVI) and Qsp/Qt increased significantly; and mean systemic pressure and heart rate were stable. Those changes were observed only in patients not treated with a beta-blocker before surgery, whereas no change occurred in patients treated with the drug. In the patients who were free from pruritus (group B, n = 28), we did not observe any significant change. CONCLUSION: The appearance of pruritus during vancomycin administration indicates that SVRI is declining, thus exposing the patient to risk for hypotension. Therapy with a beta-blocker appears to confer protection against this hemodynamic reaction.