A field experiment was conducted at El-Khatatba farm (EI-Behera Governorate) on wheat variety Sakha 69 to study the influence of some plant growth promoting rhizobacteria (Rhizobium leguminosarum, Bacillus polymyxa ) and a single yeast strain (Saccharomyces cerevisiae) as well as mixture of both on the crop yield under two nitrogen fertilizer levels (60 and 120 kg Nifed_) Nitrogenase and dehydrogenase (OHA) activi­ties were measured during the growth period. Nitrogenase activity of early stages of growth was increased, then gradually decreased with plant age. Changes in the DHAs were significant with raising nitrogen fer­tilizer level and microbial inoculation. Results indicated that the plant growth promoting rhizobacteria had a positive effect on both vegetative and yield characters (dry weight of plants and panicles). Similar trend was observed for seed yield at full dose of nitrogen fertilizer as well as nitrogen content in seeds of inoculated plants with Saccharomyces ce­revisiae and Bacillus polymyxa compared with the uninoculated control.