Various regulatory mutants of Escherichia coli have been isolated using phenylalanine and tyrosine analogues. It has been found that the growth of wild type strain of E. coli W3110 was strongly inhibited by phenylalanine analogues. Regulatory mutants resistant to phenylalanine analogue could accumulate L-phenylalanine at concentrations of 5-6 g/l. However, L-phenylalanine accumulation was increased significantly up to 11.4 g/l using a tyrosine auxotrophic mutant resistant to phenylalanine analogue such as -2-thienyl-DL-alanine.