SUMMARY Depth of anaesthesia and tendency to sleep were assessed by means of electroencephalography in healthy volunteers following the administration of different intravenous anaesthetics. Graphs of sleep depth were constructed from the records. Characteristic differences were observed in the postanaesthetic course between methohexitone, thiobarbiturates, neuroleptanalgesics, and propanidid. Whereas the effects of propanidid rapidly diminished, this was not the case with the other drugs, and even after 12 hours the potentiating effect of a small quantity of alcohol was discernible after methohexitone, thiopentone and thiobutobarbitone. The results suggest that after intravenous barbiturate anaesthesia for out-patient procedures the patient should be cautioned against driving or drinking alcohol for 24 hours, but after propanidid a 2-hour period is sufficient.