Alfathesin is a new intravenous anaesthetic agent. It is a mixture of two steroids, alphaxalone and alphadolone acetate in a ratio of 3 : 1; dissolved in an aqueous vehicle containing 20% polyoxyethylated castor oil. Alphadolone acetate has only about half the anaesthetic activity of alphaxalone but is necessary to enhance the solubility of alphaxalone.Clinical and pharmacological studies have shown Alfathesin to have a rapid onset of action and a short duration in lower doses. A single dose of 50 &mgr;l/kg has about the same anaesthetic potency as thiopentone 5 mg/kg given under the same conditions. Unlike the barbiturates, Alfathesin is rapidly cleared from the plasma; alphaxalone is conjugated in the liver and does not rely on redistribution in tissue and fat for its elimination. As a result, patients tend to recover more clear-headed than with thiopentone. Recovery is not as much delayed after incremental doses as with the barbiturates. Alfathesin has been used successfully for induction of anaesthesia which is maintained with other drugs. Cardiorespirator effects are similar to those after approximately equipotent analgesic doses of thiopentone. The incidence of venous sequelae is less than with 5 % thiopentone, 2 % methohexitone or propanidid, but similar to that with dilute barbiturate solutions.Involuntary muscle movements are the commonest unwanted effects, especially after higher doses or when hyoscine is used for premedication.