Emergency workers attending the scene of a "dirty" bomb or nuclear blast could soon have a drug to help protect them.

People exposed to radioactive material often die weeks later of acute radiation syndrome, as blood cells vital to clotting and fighting infection die off, and bone marrow cells killed by radiation cannot replace them. There is currently no preventive treatment.

Hollis-Eden Pharmaceuticals of San Diego, California, now reports that 5-androstenediol (AED), an adrenal gland hormone that stimulates marrow-cell growth, cuts the death rate among monkeys exposed to 6 grays of radiation - usually enough to kill 32 per cent of them - to 12 per cent, mainly by boosting blood platelets (International Immunopharmacology, vol 7, p 500).

The 40 monkeys were given intramuscular injections of AED 4 hours after exposure and then once daily for five days. Hollis-Eden stressed no other treatments, such as blood transfusions - which are unlikely to be widely available after a mass-casualty attack - were administered. The results suggest AED, which has already passed initial safety tests in people, may even protect victims of a blast if administered quickly enough after exposure.

Amid growing fears of terrorist attacks with radioactive materials, the US government plans to award a contract for the treatment for acute radiation syndrome later this month under its revamped BioShield fund for civilian defences against chemical, biological and nuclear threats.