The aim of this study was to investigate pain perception during thiopentone or propofol infusions for sedation. Thirty ASA 1 or 2 patients received a two step infusion of either thiopentone (step 1: 1.25 mg.kg-1 followed by 2.5 mg.kg-1.h-1; step 2: 1.25 mg.kg-1 and 12.5 mg.kg-1.h-1; n = 15) or propofol (step 1: 0.5 mg.kg-1, 1 mg.kg-1.h-1; step 2: 0.5 mg.kg-1, 5 mg.kg-1.h-1; n = 15) for sedation. At control and 10 min after the start of each infusion dosage, reaction times and thermal pain detection thresholds were determined. We found no clinically or statistically significant depression of thermal pain detection thresholds during propofol or thiopentone infusions and these are, therefore, unlikely to be associated with clinically relevant hyperalgesia.