The cumulative effects and post-anaesthetic recovery of Althesin were studied by comparing the drug with methohexitone in a series of 60 patients undergoing surgery for varicose veins. Anaesthesia was maintained with each anaesthetic agent in 30 patients by administration of intermittent doses of the respective drugs in accordance with the surgical stimulus. When repeat doses were required at intervals of 2 to 5 minutes, the fall off in requirements was observed with both anaesthetics, more distinctly with Althesin than with methohexitone. No significant difference could be observed in the time required for immediate awakening after the two drugs. However, the majority of the patients anaesthetized with Althesin displayed a peculiar lack of mental clarity for a short period after recovering consciousness. The recovery from anaesthesia was studied by various tests and observations. Recovery after Althesin appeared to proceed slightly faster than after methohexitone. When Althesin was required in high total dosage (exceeding 150 mu1/kg), the immediate awakening was associated with emotional upset and confusion. Frequency of nausea and vomiting after anaesthesia was considerably higher in the Althesin group than in the methohexitone group. These symptoms might be toxic due to the excessive dosage given. Using the induction time as a basis for calculation of the potency ratio, Althesin and methohexiton were found to have the ratio of 1:33 (expressed in mu1/kg : mg/kg).