Equine neutrophils were isolated from the blood of horses and combined with the contagious equine metritis organism (CEMO) or CEMO cell wall constituents to evaluate the response of this leukocyte. The interaction of neutrophils and these agents was evaluated using bacteriological, ultrastructural, light microscopic, and biochemical methodologies. Blood neutrophils were also evaluated ultrastructurally and morphometrically after separation on two Ficoll-hypaque gradients at 4(DEGREES)C and 22(DEGREES)C. Isolation procedures at both temperatures resulted in degranulation but not neutrophil swelling. Cells isolated at 22(DEGREES)C had the most extensive degranulation. This study indicated that isolation of equine blood neutrophils at 4(DEGREES)C resulted in minimal cell degeneration;Phagocytosis and intracellular killing of CEMO was evaluated by combining neutrophils with CEMO or Escherichia coli in high- and low-specific antibody titer serum or genital secretions. More E. coli than CEMO were phagocytized at each time period. After 210 minutes of incubation, more CEMO than E. coli were killed by equine neutrophils in serum; more E. coli than CEMO were killed by neutrophils in genital secretions. These studies suggest CEMO is a extracellular pathogenic bacterium and that immunoglobulins in genital secretions from nonimmune horses do not enhance CEMO phagocytosis or intracellular killing;Equine neutrophils were combined with CEMO or one of two isolated CEMO lipopolysaccharides (LPS-a; LPS-p) to evaluate the effect of these agents on neutrophil morphology and function. Neutrophils exposed to CEMO had more cytoplasmic granules than did neutrophils exposed to either of the CEMO lipopolysaccharides. Neutrophil iodination was increased by LPS-a but not significantly changed by LPS-p or CEMO. Nitroblue tetrazolium reduction and staphylococcus aureus ingestion were significantly increased by LPS-p at a high dosage level. These results suggest that the effects of CEMO on equine neutrophils may be partially a result of CEMO cell wall lipopolysaccharides.