A new Burkholderia strain (PVFi5A) which exhibits antagonism towards many bacterial and fungal plant pathogens has been partially characterised. This strain was isolated from the rhizosphere of tomato plants and was referred to the Burkholderia cepacia complex on the basis of cultural, morphological and biochemical characteristics, including determination of the 16S ribosomal DNA sequence and fatty acid profile. Strain PVFi5A is a Gram-negative, aerobic bacterium, oxidase- and catalase-positive, motile with a polar tuft of flagella, able to grow on a variety of media without producing diffusible pigments; it is avirulent to onion, able to grow at 41 degrees C and resistant to several antibiotic substances. Its fatty acid profile contains the hydroxy acids 18:1 20H, 14:0 3OH and 16:0 3OH, but not the hydroxy acids 16:0 2OH. The antagonistic activity of strain PVFi5A is due to its production of various, as yet unidentified, antimicrobial compounds, one or more of which may differ from those reported previously for certain 'B. cepacia' strains. The ability of PVFi5A to suppress the growth of important bacterial and fungal phytopathogens makes this strain a potential biocontrol agent.