Our investigations pointed out the existence of a high variability of some biochemical indices in the hepatic, muscular and blood tissue at Rana ridibunda Pall. and Rana esculenta L. Higher amounts of sugars and transaminases were found in the tissues of Rana esculenta L. species, while Rana ridibunda Pall. was characterised by higher levels of fats (triglycerides and cholesterol). With some exceptions, the highest values of the analysed biochemical indices were found in blood. The electrophoresis of plasma blood proteins of the two species of green frogs showed the presence of 3 4 proteic fractions in blood. The albuminic fraction at Rana esculenta L. contains two sub-fractions, and this fact sustains the idea of a hybrid nature of this species.