Specimens of Plagiorchis noblei from Tyrannus tyrannus and T. verticalis, were analyzed for morphological differences using multivariate techniques. Hotelling's T2-test showed a highly significant difference (P less than 0.001) between the two parasite populations. A stepwise discriminant analysis selected pharynx and testis as the characters that best separated the two populations, and correctly classified 69% of the specimens as to their host species. Plagiorchis gonzalchavezi was determined to be a junior subjective synonym of P. noblei.