Both polyclonal and monoclonal antibodies have been developed to Pseudomonas solanacearum, the causative agent of bacterial wilt. When used in an indirect enzyme-linked immunosorbent assay, the polyclonal antibodies detected as few as 1 X 104 bacterial cells ml-1 in infected plant or soil samples, but they could not distinguish between P. solanacearum, P. celebensis, P. syzygii and P. picketti. The monoclonal antibodies developed had differing specificities, but, using selective immunization schedules, several were obtained which no longer cross-reacted with closely related bacteria. These monoclonal antibodies were not as sensitive as the polyclonal antibodies and were only able to detect down to 1 X 106 cells ml-1.