Abstract: The present invention relates to pharmaceutically active ornithine compounds, particularly to pharmaceutically acceptable ammonium salts of N?-acyl derivatives of N?(4-amino-4-deoxypteroyl)-L-ornithine compounds; and methods of treatment and pharmaceutical compositions that utilize or comprise one or more of such ammonium salts. The ammonium salts provided by the invention exhibit superior chemical stability than corresponding acidic N?-acyl derivatives of N?-acyl derivatives of N?(4-amino-4-deoxypteroyl)-L-ornithine compounds.