Drawbacks of intensive farming practices and environmental costs of N fertilizers have renewed interest in bio-fertilizers. This study was conducted in order to investigate the effectiveness of 7 N-2-fixing bacterial isolates from various sources in sugar beet and barley production under field conditions in the higland plateau of Erzurum, Turkey (29 degrees 55' N and 41 degrees 16' E with an altitude of 1950m) in 1999 and 2000. Seeds were inoculated with five bacterial strains of Bacillus; BA-140, BA-142, M-3, M-13, and M-58, a strain of Burkholderia (BA-7) and Pseudomonas (BA-8). The bacterial strains had been demonstrated to grow in N-free basal medium. The experiment also included applications of mineral nitrogen (N), phosphorous (P), and NP-fertilizer as well as a control treatment without inoculation and fertilizer application.