Pseudomonas fluorescens is a plant growth-promoting rhizobacterium. Certain strains of Pseudomonas fluorescens produce secondary metabolites that are toxic to plant-pathogenic fungi. It is not surprising, therefore, that the production of antifungal compounds enhances the ability of these bacteria to suppress a variety of plant diseases and in some instances contributes to the ecological competence of the producing strain within the rhizosphere. Specific strains of Pseudomonas fluorescens & Pseudomonas putida provide biological control of fungal plant pathogens and deleterious rhizobacteria with concomitant positive growth responses above & beyond simple amelioration of disease. The ability of these strains to act as biological control agents has been attributed to their ability to rapidly & competitively colonize roots & to produce siderophores (iron-binding compounds) and antibiotics. The first of these biological control formulations based on Pseudomonas has been placed into the field for commercial control of damping-off fungi on cotton. Pseudomonads produce a host of antibiotics including phenazines, pyrroles, pseudomonic acid, pyo compounds and amino acid-containing antibiotics.