Background: Alkaline phosphatase is an enzyme hydrolyzing monophosphate esters. The main pathologies associated with its increased activity include diseases of the liver and the skeletal system.Dramatic increases of alkaline phosphatase activity occur in infants and young children in transient hyperphosphatasemia. Material/Methods: The clinical course of 4 cases of hyperphosphatasemia in infants and young children was analyzed. The diagnoses were based on the criteria described by Kraut et al. Results: In the reported cases, increases of alkaline phosphatase activity, usually of both isoenzymes, were diagnosed accidentally during investigations performed for other reasons. The onset of the disease was preceded by infections. Other laboratory results were within normal limits specific for the patients’ age. Spontaneous normalization of alkaline phosphatase activity levels was observed during the next 2 –3 months.Conclusions: Transient hyperphosphatasemia of infants and young children is a benign condition, subsiding spontaneously without treatment. The management should be limited to periodic check-ups of alkaline phosphatase activity.

Keywords: Alkaline Phosphatase, hyperphosphatasemia, infants and children