Sir.—Recently, Reif et al1described 50 children and adolescents with gallstones and discussed the conditions associated with the development of gallstones in children, with the exception of erythropoietic protoporphyria (EPP). Of the two most common porphyrias, EPP rivals porphyria cutanea tarda in prevalence, and is characterized clinically by photosensitivity commencing in childhood and biochemically by excessive amounts of red blood cell protoporphyrins.2Protoporphyrin is excreted in the bile and gallstones, which are partially composed of protoporphyrin and have been reported in about 12% of patients with EPP who are liable to produce symptoms at an unusually early age.3Determination of the protoporphyrin solubility in the bile and the mechanism by which gallstones form in patients with EPP is poorly understood. Results of scientific research on rat models have shown that biliary protoporphyrin excretion depends on bile acids and, if bile acid excretion rates decrease, biliary