The mechanism by which Burkholderia pseudomallei survives in macrophages is not clearly understood. In this study, we demonstrated that the mouse macrophage cell line (RAW 264.7) treated with lipopolysaccharide (LPS) from B. pseudomallei (BP-LPS) produced significantly less NO and TNF-alpha compared with those stimulated with the LPS from Escherichia coli and Salmonella typhi. The time required for the BP-LPS to trigger substantial NO and TNF-alpha release was at least 30 min, compared with < 5 min for the E. coli-LPS. A time course study of inducible nitric oxide synthase (iNOS) protein expression also indicated that the time required for macrophages stimulated with the BP-LPS to up-regulate iNOS was longer. The longer time lag for the BP-LPS to activate macrophages was probably due to the delay in up-regulation of iNOS and TNF-alpha mRNA transcription. These results indirectly suggest that the delay of the mediators' production may be due to a reduced rate of signal transduction initiated by the interaction of BP-LPS with the macrophage cell surface. The use of MoAb to phosphorylated p38 in a Western blot analysis provided data compatible with the notion that the maximum level of phosphorylated p38 from the cells activated with BP-LPS was attained at a slower rate. These results suggest that the unique structure of BP-LPS exhibits a property which may interfere with macrophage cell activation.