AThe invention relates to 3a ethynyl 3 hydroxy 5a pregnan 20 oxime or a pharmaceutically acceptable salt thereof which compounds and/or salts are useful as modulators of the mammal brain excitability via the gamma 5 aminobutyric acid receptor chloride ionophore (GABA R) complex and in the treatment of disorders such as hepatic encephalopathy Down s syndrome and Alzheimer s disease.