Inherited metabolic disorders are individually rare but as a whole, they are nor rare. Since Archibald Garrod introduced a concept of "inborn error of metabolism" or "chemical individuality", more than 600 diseases are currently known, affecting approximately one in 500 newborns cumulatively. They frequently manifest with acute, life-threatening crisis that requires immediate specific intervention or they present with insidious diverse symptoms and signs involving multiple visceral organs or tissues as well as central nervous system, hampering a correct diagnosis. In addition, many pediatricians are not familiar with all diagnostic and therapeutic strategies for diverse inherited metabolic disorders. However, the prognosis of affected children are heavily dependent on rapid and effective treatment. In this lecture, practical guidelines for the specific diagnosis based on diverse clinical features of inherited metabolic disorders will be described. Many sophisticated laboratory tests are available for the confirmatory diagnosis of each disease, which is challenging to general pediatricians with respect to knowledge about biochemical metabolite assay test, enzymatic test and DNA diagnostic tests. Sample collections, indications, methods and interpretation of results in varying laboratory tests will be listed as well.