Field experiment was carried out at El-Bagour, Minofia governorate during 2003 and 2004 seasons. This experiment aimed to study the effect of antagonistic strains (Trichoderma harzianum, Bacillus subtilis and Streptomyces aureofaciens in combination with Azotobacter chroococcum on growth and yield of tomato. Obtained results showed that dual inoculation with either A. chroococcum + B. subtilis or A. chroococcum + T. harzianum showed lower percentage of disease rate and disease severity of tomato plants. The highest values of were observed in the treatment of inoculation with A. chroococcum combined with B. subtilis + T. harzianum. Also, tomato inoculation with A. chroococcum combined with B. subtilis + T. harzianum gave the highest records of growth characters, yield and yield components of tomato. In view of the obtained results, it can be concluded that the dinitrogen
fixers and bicontrol agents can be used for improving the quantity and quality of tomato production .

Key words: Tomato, biofertilization, biological control, damping-off and root rot, dehydrogenase and nitrogenase.