The variability of nine morphometric parameters of Leucocytozoon simondi, L. dubreuili, and L. fringillinarum was studied with respect to variability (a) within a single bird; (b) within a single bird at different times; (c) between different birds of the same species: (d) between the same species of birds of different populations; and (e) between different species of birds. The results indicated that the variability of the parasites was of the same order of magnitude for all situations studied. Leucocytozoon dubreuili, L. fringillinarum, and the round phase of L. simondi could not be separated on the basis of measurements alone. It was concluded that the morphometric characteristics were not valid criteria for species differentiation. These studies result in the proposed synonymy of Leucocytozoon anseris with L. simondi, and of L. anellobiae, L. bouffardi, L. cambournaci, L. gentili, L. monardi, L. roubaudi, and L. seabrae with L. fringillinarum.