In two field experiments, wheat was inoculated with various strains of Azospirillum spp. The two A. brasilense nir− strains isolated from surface-sterilized wheat roots increased the number of Azospirillum in surface-sterilized roots, plant dry matter, and percent N. The total N accumulated in plant tops at heading stage was increased by 30% in the first experiment (strain Sp 107 st) and by 51 and 89% (strains Sp 107 st and Sp 245, respectively) in the second experiment. The Azospirillum numbers (MPN) in chloramine-t treated roots were correlated with total nitrogen accumulation in plant tops (r = 0.92**). Numbers of Azospirillum in nonsterilized roots did not correlate with total plant N accumulation.