Clavicipitic acid, a metabolite of Clauiceps strain SD 58, is a mixture of isomers, the major one of which was shown by a single-crystal X-ray analysis to give structure IIa. It is formed from tryptophan and mevalonic acid but is not further converted into the tetracyclic ergot alkaloid elymoclavine. Its formation represents a derailment of ergoline biosynthesis after the first pathway-specific step, the isoprenylation of tryptophan. In this paper we report results which unequivocally confirm structure I1 for clavicipitic acid and define its stereochemistry. In addition biosynthetic data pertaining to the formation of clavicipitic acid and its role in ergoline biosynthesis are presented and discussed.