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Two species of green frogs exist in the state of Bavaria (Germany), the Marsh Frog (Pelophylax ridibundus) and the Pool Frog (Pelophylax lessonae). The Edible Frog (Pelophylax esculentus) is a hybridogenetic hybrid originally resulting from Marsh Frogs mating with Pool Frogs and therefore sometimes not considered a true species. Its distribution covers large parts of Bavaria, occurring either together with P. lessonae in P. lessonae-P. esculentus-systems (LE-system) or with P. ridibundus in P. ridibundus-P. esculentus-systems (RE-system). In order to obtain more precise data on their distribution and population structure, we examined 20 green frog populations in Bavaria, focusing on the possible existence of pure hybrid populations, the occurrence of allochthonous species of green frogs, and the distribution of P. lessonae, the most threatened species of green frogs. A total of 200 frogs were sampled, from which 173 could be reliably identified on the basis of their morphology. Species were identified via morphometric measurements and serum albumin PCR. Potentially triploid specimens were identified on the basis of their increased erythrocyte size. Sequencing of mitochondrial ND2 haplo types allowed identification of allochthonous frogs in three study sites. P. esculentus was the most common green frog species at the study sites, representing 47% of the sample size. Four potentially triploid individuals were detected; however, pure triploid hybrid populations could not be confirmed. Allochthonous frogs were identified in three RE-systems. Pelophylax ridibundus made up 38% of the reliably identified frogs. The percentage of P. lessonae was …