Bacterial blight is a major disease of coriander caused by Pseudomonas syringae pv. coriandricola. The nature of this disease was studied by inoculating coriander plants with rifampicin resistant P. s. pv. coriandricola. All inoculated plants showed disease symptoms and the level of mortality was significant. The pathogen was isolated from different parts of inoculated coriander plants implying internal infection. Macroscopic inspection of diseased plants showed blackening of leaf veins and surrounding tissues. Closer examination confirmed the presence of large numbers of bacterial cells within leaf veins. Examination using light and electron microscopy showed infected coriander stem tissue contains large numbers of bacteria within xylem vessels and neighbouring pith cells. The interstitium of infected plants also contained large bacterial populations. Isolation and culture of bacteria from infected tissues confirmed the identity of the pathogen observed. No bacterial cells were seen within phloem vessels or below the inoculation site. These results suggest that the coriander pathogen utilizes the vascular system of the host for multiplication and transport, leading to infection of many tissues and, potentially, host death.