This experiment was performed to study effects of Azospirillum brasilense inoculation on the protein bound amino acid concentration in wheat, barley, peas and lupin at 30, 60 and 90 days after planting. Cereals were inoculated with Azospirillum, legumes were inoculated with either Rhizobium or with Azospirillum or with a mixture of both inoculants, uninoculated plants were used as control. Amino acids were extracted and measured in both roots and shoots of plants. Results indicate that, the concentrations of amino acids were generally higher both in roots and shoots in all plants inoculated with Azospirillum in spite of the plant age. In legume tissues, the highest concentration of amino acids obtained in plants inoculated with a mixture of both inoculants, followed by Rhizobium, then Azospirillum. The differences in amino acid concentrations between Azospirillum inoculated and uninoculated treatments Were more clear in the early stage of growth. There are essentially no qualitative differences in the known amino acids in the tissues of both roots and shoots wether inoculated or uninoculated plants.