The possibility of incorporation of 5-fluorotryptophan into ergot alkaloids by Claviceps purpurea PRL 1565 was explored utilizing randomly tritiated material. Very little radioactivity was found in the alkaloid fraction, most of it residing either in the mycelium or in the base-soluble fraction which would contain unchanged 5-fluorotryptophan. Thin-layer chromatography allowed the isolation of an alkaloid containing radioactivity, but fluoride analysis using neutron activation indicated the absence of fluorine in the molecule. It was concluded that 5-fluorotryptophan was not incorporated into the ergot alkaloids produced by C. purpurea PRL 1565.