The influence of a range of amino acid additives on the crystallization Of L-glutamic acid has been investigated. The presence of a bulky side chain (phenyl) in L-phenylalanine and L-tyrosine was identified as an essential feature in achieving stabilization of the alpha-polymorph at low additive concentrations. Minute quantities of these additives were incorporated into the alpha-L-glutamic acid product crystals when the additive/L-glutamic molar ratio was 1:30 in solution; in this condition no beta-form inclusions were observed inside the alpha-form crystals. At higher additive/L-glutamic acid molar ratios in solution (1:6), a significant amount of additive uptake was observed and changes in a-form morphology were noted under these conditions. A key feature was the disappearance of the {011} and {001} facets of alpha-L-glutamic acid and the emergence of the {111} and {110} facets. The overall hypothesis is that additives disrupt the developing beta/alpha interface and this stabilizes the alpha-form.