Androstenediol, or 5-androstenediol (abbreviated as A5 or Δ5-diol), also known as androst-5-ene-3β,17β-diol, is an endogenous weak androgen and estrogen steroid hormone and intermediate in the biosynthesis of testosterone from dehydroepiandrosterone (DHEA).

Androstenediol is a direct metabolite of the most abundant steroid produced by the human adrenal cortex, DHEA.

Its value as a radiation countermeasure is based mainly on its stimulation of production of white blood cells and platelets.

[6] Its potential use as a radiation countermeasure was developed by the Armed Forces Radiobiology Research Institute (AFRRI) and subsequently studied by AFRRI and Hollis-Eden Pharmaceuticals under the proposed brand name Neumune for the treatment of acute radiation syndrome.

[8] Hollis-Eden had applied for a contract from the U.S. Government under the BioShield Request for Proposals (RFP) for radiation countermeasures.