Benign transient hyperphosphatasemia (BTHP) was diagnosed in nine children who were examined in the Pediatric Department at Beilinson Medical Center during 2 years. The characteristic features of this disorder are: a) elevation of serum alkaline phosphatase (AP) of 3-50 fold the upper normal value for age, usually discovered during mild upper respiratory or gastrointestinal infection, and sometimes by routine laboratory workup; b) no clinical or laboratory evidence of bone or liver disease; c) the elevated AP is of liver and bone origin; and d) AP returns to normal range within 12 weeks. BTHP usually occurs in infants but may appear also in adults. Recognition of this benign entity will prevent extensive unnecessary laboratory workup.