(-)-Verrucosan-2β-ol (C20H34O), a rare diterpene with a 3,6,6,5-tetracyclic ring system, has been isolated and identified for the first time from the phototrophic bacterium Chloroflexus aurantiacus. Furthermore, an unsaturated diterpenoid hydrocarbon (C20H32) with a similar carbon skeleton was found in the same organism. This prokaryote, naturally occurring in hot spring microbial mats, is considered to be one of the oldest bacterial life forms on earth. Verrucosane-type diterpenoids had previously been detected only in some liverworts (Hepaticae), forming a unique group in the plant kingdom.