This study explored the effectiveness of non-indigenous and indigenous Azotobacter chroococcum strains on yield response and N concentrations of spring wheat cultivation under greenhouse and field conditions in Merzifon, Turkey. The non-indigenous, A. chroococcum strain Beijerinck 1901 (DSMZ 2286), was tested in the study. Ten indigenous strains of A. chroococcum were isolated from various sources in Northern Anatolia, Turkey. Seeds of wheat (Triticum aestivum) were inoculated with 11 bacterial strains of A. chroococcum; Beijerinck 1901, RK33, RK34, RK38, RK39, RK40, RK41, RK46, RK48, RK49 and RK50. Plants were harvested for 83 days in pots and 106 days in plots after sowing. Research result showed that all A. chroococcum strains had positive effect on the yield and N concentrations of wheat. Also, indigenous strain A. chroococcum RK49 had the highest effects on yield and increased the production of grain yield by 84% in field experiment and by in 95% pot experiment compared to control treatment without A. Chroococcum inoculation. Based on the research results, it was suggested that the use of indigenous A. chroococcum strains might be suitable when producing and using bio-fertilizer. (c) 2008 Elsevier B.V. All rights reserved.