Strains representing the fluorescent plant pathogenic Pseudomonas spp., Ps. agarici, Ps. asplenii, Ps. avellanae, Ps. beteli, Ps. caricapapayae, Ps. cichorii, Ps. corrugata, Ps. ficuserectae, Ps. flectens, Ps. fuscovaginae, Ps. marginalis, Ps. meliae, Ps. savastanoi, Ps. syringae, Ps. tolaasii and Ps. viridiflava were tested for biocidal activity using Aspergillus niger as assay organism. Inhibitory behaviour was found in strains of Ps. asplenii, Ps. blatchfordae, Ps. cichorii, Ps. corrugata, Ps. fuscovaginae, Ps. marginalis, Ps. marginalis pv. pastinacea, Ps. syringae pv. syringae, Ps. syringae pv. aptata, Ps. syringae pv. atrofaciens, Ps. syringae pv. lapsa, Ps. tolaasii, and strains of a Pseudomonas sp. pathogenic to Actinidia, in the Ps. savastanoi genomic sp. Antifungal activity could be identified with the production of members of the syringomycin family of toxins by strains in Ps. syringae, Ps. asplenii and Ps. fuscovaginae. These toxin reactions support suggestions made elsewhere of the synonym of the latter two species. In a preliminary characterization using tests for stability to heat, protease, acid and alkaline treatments, unknown toxins consistent with syringomycin-like toxins the strains from Actinidia species. The toxins from Ps. cichorii and from Ps. corrugata differed in their reactions from all other agents. Pseudomonas tolaasii produces the antifungal compound tolaasin. The white line reaction with Ps. reactions, a test for tolaasin production by strains of Ps. tolaasii, was confirmed as specific for this compound. Some of these low molecular weight toxins may be produced by some of these plant pathogenic strains.