Ninety one bacterial strains isolated from the rhizosphere of maize, wheat, clover and rice plants were screened for their plant growth promoting activities. The results of in vitro assays showed that all rhizobacterial isolates had the ability to produce indole acetic acid (IAA) in presence or absence of tryptophan (L-TRP) with a wide variation observed among them. Auxin production, however, by some isolates was enhanced when culture media were supplemented with L-TRP. The results also showed that 11 rhizobacterial isolates were able to solubilize calcium super phostphate Ca3 (PO4)2 on Bunt and Rovira medium. These isolates were tested for nitrogenase activity and cyanide production. Consequently, the more efficient isolates, namely Wh5 and Rh6 were identified to the species level in Cairo MIRCEN (ASU) as Micrococcus luteus and Bacillus licheniformis and isolate Mh4 was identified by 16S rRNA analysis as Pseudomonas aeruginosa. The antimicrobial activity of the four selected plant growth promoting rhizobacteria (PGPR) was assayed against six phytopathogenic fungi and two phytopathogenic bacteria. P. aeruginosa showed the most powerful effect against all the tested fungi and Erwinia carotovora pathovar carotovora. Also, these four selected PGPRs were tested as bio-inoculants for maize plants in pot experiments. The results showed that the application of bio-inoculants alone or combined with half of the recommended dose, significantly increased the dry weight of both shoots and roots of maize plants. [ABSTRACT FROM AUTHOR]