Seizure duration in unilateral electroconvulsive therapy (ECT) was recorded by means of EEG in an intraindividual comparison of etomidate (dissolved in a soy-bean oil emulsion) 0.3 mg/kg and Althesin (alphaxalone 9 mg and alphadolone 3 mg/ml) 0.6 mg/kg with methohexitone 1 mg/kg body weight. The patients were intubated and alveolar CO2- and O2-concentrations kept constant at 3% (3 kPa) and 92% (92 kPa) respectively. Seizure duration was the same when either etomidate or methohexitone were used, whereas Althesin significantly shortened seizure duration in comparison with methohexitone. Local pain on injection and a subsequent superficial thrombophlebitis occurred frequently with methohexitone. This did not occur with etomidate or Althesin.