Biosynthesis of the three aromatic amino acids (l-phenylalanine, l-trypto phan, l-tyrosine) and its regulation in Escherichia coli and corynebacteria are reviewed. The common aromatic biosynthetic pathway (shikimate pathway) starts with the condensation of phosphoenolpyruvate and erythrose 4-phosphate. Through six biosynthetic steps the pathway proceeds via shikimate to chorismate, from which the terminal pathways to tryptophan, phenylalanine and tyrosine branch. The first step in the common pathway is performed in E. coli by three isoenzymes, which are specifically feedback-inhibited by the three terminal products.