Two-dimensional gel electrophoresis was used to identify differentially displayed proteins during treatment of Xanthomonas axonopodis pv. passiflorae in media containing leaf extract of the compatible (passion fruit) and incompatible (tomato) hosts. The results showed that at different times of treatment (5, 25 and 45 h) the global expression of proteins was almost identical in cells grown in minimal medium (MM) and in medium containing leaf extract of the incompatible host (MMT). The protein patterns of cells grown in medium containing passiflorae (MMP) leaf extract and MM were also compared enabling the detection of 17 differential spots. Most of the proteins were induced at earlier times of incubation (5 h) and maintained until 45 h in MMP. By using another carrier ampholyte range, seven additional proteins were identified in MMP treated cells. Five proteins, including one constitutive, two induced and two up-regulated in MMP were microsequenced. All sequences were found in the genome of xanthomonads sharing high level of identity (88-100%). Fructose biphosphate aldolase was expressed in all media employed. A putative membrane-related protein and a hypothetical protein were novel proteins induced specifically by the passiflorae extract. An inorganic pyrophosphatase and a hypothetical protein that showed similarity to the yciF gene of Salmonella thyphimurium were up-regulated in MMP.