During the two growing seasons, nitrogen, phosphorus and potassium concentrations and their content of potato shoots were negatively affected by decreasing NPK dose less than the recommended one (control).However,                bio-fertilizers application, overall NPK dose, significantly increased N, P and P concentrations and their contents. The most effective strain was found with NFB when used individually or incombination with the otherstrains used. Therefore, NFB+PDB+SB recorded high values regarding N, P and K  concentrations and their content.                 The interaction treatments, indicate that, bio-fertilizers counteracted the depressing effects of NPK stress and showed an increase in N, P and K concentrations and their content in potato shoots. On the other hand, No₃^-concentration and nitrate reductase activity  (NRA ) were decreased whereas, free amino acids were increased. Inoculation with the three bacterial strains used recorded best results  in this respect.