Allopregnanediol, or 5ñ-pregnane-3ñ,20ñ-diol, is an endogenous metabolite of progesterone and allopregnanolone and an isomer of pregnanediol (5ò-pregnan-3ñ,20ñ-diol). It has been found to act like a partial agonist of an allosteric site of the GABA receptor and hence might play a biological role as a neurosteroid. It has also been found to act as an agonist of the human pregnane X receptor, albeit with an EC<sub>50</sub> that is more than an order of magnitude lower than that of other endogenous pregnanes like pregnenolone, pregnanediol, allopregnanedione, and allopregnanolone.