The absorption and sedation following an intranasal dose of sufentanil were evaluated and compared with those of the same dose given intravenously. Sixteen adult patients scheduled for elective surgery were randomly allocated to receive as premedication 15 micrograms sufentanil either intravenously or intranasally. Before administration and at fixed time intervals thereafter, the degree of sedation was assessed, vital signs were recorded and venous blood samples were taken for the determination of sufentanil plasma concentrations. Peroperative sedation of rapid onset and limited duration was seen in both groups. However, the onset of sedation was more rapid after intravenous injection. At 10 min, all patients in the IV group were sedated versus only two in the intranasal group (P less than 0.01). No significant intergroup differences in sedation were seen at 20 to 60 min. This clinical effect is in agreement with the measured plasma levels, which were significantly lower after intranasal application at 5 and 10 min, being 36 and 56 per cent of those after IV dosing, respectively. From 30 min, plasma concentrations were virtually identical for the two routes of administration. The AUC0-120 min after intranasal dosing was 78 per cent of that after intravenous injection. Intranasal dosing induced no clinically significant changes in vital signs, whereas after IV sufentanil, a clinically significant decrease in PaO2 was seen at 5 min. The results of this study show that sufentanil, when administered intranasally, is rapidly and effectively absorbed from the human nasal mucosa, so that this route may be an attractive alternative for a premedicant, avoiding the discomfort of an intravenous or intramuscular injection.