Abstract: Solutions of three amino acids (serine, glycine and proline) were analyzed under varying reaction conditions for their interferences in ammonium-N determination using the Berthelot indophenol colour reaction. The results regarding the changes made in the reaction conditions revealed that freshly prepared reagents should be used in studies investigating interferences by amino acids. Room temperature should be stable or reagents bottles should be placed in a water bath having a constant temperature of 25°C. The hypochlorite reagent should be freshly prepared at a concentration of 50 ml l–1.