To increase the in vivo output of a chosen metabolite requires the increase of a number of enzyme concentrations. The enzymes are identified as those leading directly from output back to the input(s). This identification will reveal a number of branch points leading to other parts of metabolism which should not be perturbed. A simple calculation gives the enzyme multipliers, factors by which the identified enzyme concentrations should be increased to generate a given increase in the output flux. The net result of this procedure will be to extract any desired increase in flux while leaving the rest of metabolism to growth and other important functions of the cell unchanged. The method is entirely general.