In 34 subjects undergoing topical anaesthesia with lidocaine gel (2% xylocaine gel), the concentrations of lidocaine base were measured in repeated venous blood samples. Twenty-three patients (Group I) were given 20 ml of 2% lidocaine gel (400 mg of lidocaine) and six subjects (Group II) 40 ml of 2% lidocaine gel (800 mg of lidocaine) nasopharyngeally, the gel reaching the pharynx being swallowed. Five minutes after administration of the gel, a gastric tube was introduced via the nasal cavity. In six patients (Group III), the bladder was catheterised in addition to insertion of a gastric tube. Before the catheter was introduced, these patients were given lidocaine gel nasopharyngeally (400 mg) and endourethrally (400 mg). After the introduction of the gastric tube, all subjects (except four volunteers in Group II) were given general anaesthesia. Before intubation, the patients in Group III also received lidocaine spray laryngotracheally (50 mg; 10% xylocaine spray). The initial absorption of lidocaine was rapid, although the blood concentrations were low. The mean peak concentrations (Cmax) of lidocaine in the three groups were 0.57, 1.39 and 0.73 micrograms/ml, respectively. The blood concentration in Group II was significantly higher than those in Groups I and III. The mean length of time between the nasopharyngeal application of lidocaine gel and the time when Cmax was reached (tpeak) was the same in all three groups (60-70 min).(ABSTRACT TRUNCATED AT 250 WORDS)