Geldanamycin is an ansamycin consisting of a 19-membered macrocyle incorporating a benzoquinone ring and a lactam functionality. It shows antimicrobial activity against many Gram-positive and some Gram-negative bacteria. It has a role as an antiviral agent, an antineoplastic agent, an antimicrobial agent, a cysteine protease inhibitor and a Hsp90 inhibitor. It is an ansamycin, a carbamate ester, an organic heterobicyclic compound and a member of 1,4-benzoquinones.