Electrophysiological techniques were used to study active ion transport across the skin in larval, pedomorphic and metamorphosed alpine newts (Triturus alpestris apuanus).Data were compared with morphological and histoenzymological studies (alkaline phosphatase ‐ APH ‐) in the skin of the same animals. A short circuit current, which presumably corresponds to active sodium transport, apparently absent in larvae, develops in pedomorphic specimens during the adult epidermis differentiation process and appears to be sensitive to some extent to temperature changes. Flask cells appear early in pedomorphic forms and reveal intense APH activity, a characteristic which is also found in adult animals. Circumstantial evidence correlates APH activity with transport phenomena. These findings support the hypothesis that morphological and physiological differentiation form part of a single process occurring during metamorphosis.