Inconsistencies in the attractiveness of synthetic samples of gyptol and gyplure prompted a reinvestigation of their physical, chemical, and biological properties. Although produced by the female gypsy moth, Porthelria dispar (L.) pure gyptol, d-10-acetoxy-cis-7-hexadecen-1-ol, appears to be sexually inert toward the male moth, as does the synthetic homologue, gyplure. The structure previously assigned to the natural sex pheromone must be considered as incorrect.