Lidocaine is often used as a topical analgesic prior to painful procedures performed in the oral cavity and upper airways. In this study the optimal time interval for performance of painful procedures in the oral cavity and the upper airways was determined by spraying lidocaine solution on the mucous membranes of the mouth with subsequent measurements of pain thresholds induced by argon-laser stimulation. Two different dosages (30 mg and 60 mg) of lidocaine spray were administered to the oral mucosa of the lower lip in healthy volunteers. Repeated measurements were performed until normal sensitivity returned after 15 min. Pain thresholds increased 62% after 30 mg lidocaine and 50% after 60 mg lidocaine (a non-significant difference). Thus repeated applications were found to be without any additional hypoalgesic effect. Maximal hypoalgesia was reached after 4 to 5 min. Complete analgesia was not obtained. The hypoalgesic effect lasted until 14 min, but painful procedures should be performed in the time interval 3-8 min after application.