Though simple in idea and technical design - and low in traffic volume (about 1 to 10 postings a day) - it has become quite a unique phenomenon in the area of Inborn Errors of Metabolism: By December 2017 (in its 23rd year) Metab-L had a subscription base of over 1700 subscribers worldwide, which is still growing on an almost daily basis. Although of initially European-German origin, Metab-L members today come mainly from the USA and the UK with growing participation by scientists from all parts of the world. Inborn error of metabolism specialists taking part in Metab-L are mostly clinicians/ pediatricians or coming from a biochemical and laboratory professional or geneticist background. A great portion of members of the most important metabolic scientific societies, SSIEM and SIMD, regularly participate in Metab-L discussions. The renowned "Journal of Inherited Metabolic Disease" now explicitly publishes "summaries of contributions e.g. to the metabolic Email list metab-l" and in other places, as well, Metab-L is regularly cited in scientific literature: Example articles with Metab-L citation.