The synthesis of 1-aminoalkylphosphonous acids, isosteres of the protein amino acids, by addition of hypophosphorous acid to diphenylmethylimines is described. These analogues of glycine, alanine, valine, leucine, isoleucine, phenylalanine, tyrqsine, tryptophan, serine, threonine, methionine, cysteine, cystine, glutamic acid, lysine, ornithine, arginine, and proline have been prepared and the analogues of alanine, valine, leucine, phenylalanine, and methionine resolved. Tha alanine, valine and methionine analogues have interesting antimicrobial activity and the alanine analogue has plant growth inhibiting properties. Oxidation of the appropriate 1-aminoalkylphosphonous acids gave the 1-aminoalkyl-phosphonic acid analogues of (±)-alanine, (–)-alanine, (±)-valine, (–)-valine, (±)-serine, (±)-threonine, (±)-lysine, (–)-leucine, and (±)-ornithine.