The variability and diagnostic usefulness of morphological features of metacercariae of two Diplostomum species, D. spathaceum and D. mergi, were studied on 104 and 85 specimens, respectively. Metacercariae were experimentally raised from cercariae in carp fry, Cyprinus carpio. Fourteen morphometric features and eight indices have been analysed. While no single variable could provide a classification with a reasonably small percentage of error, D. spathaceum and D. mergi have been separated with a misclassification rate less than 1% by applying a logistic regression model based on six significant variables (five metrical features and one index).