Pasteurella haemolytica antigenic extracts were made, using saline solution, potassium thiocyanate (KSCN), and sodium salicylate (SS) extraction procedures. Of the 3 techniques, saline solution extraction resulted in the lowest protein concentration and lowest ribonucleic acid-to-protein ratio. The extracts varied in protein:carbohydrate ratios, with the KSCN extract being highest and the saline solution extract the lowest. Each extract contained lipopolysaccharide, as determined by detectable quantities of 2-keto, 3-deoxyoctonate. The saline solution extract contained the fewest protein bands by sodium dodecyl sulfate-polyacrylamide-gel electrophoresis, but contained the highest molecular weight proteins. All 3 extracts were reasonably similar antigenically, as detected by immunoblotting. Many of the protein bands present in the KSCN or SS extracts did not seem to be antigenic. Each extract was subjected to chromatofocusing, and the greatest antigenic peak, for each extract, failed to bind to the exchanger. These highly antigenic peaks, designated as saline solution, KSCN, or SS antigens, were similarly high in carbohydrate content, had similar antigenic-profiles, and contained high molecular weight (greater than 200,000) antigenic material, most likely carbohydrate in nature, as detected by immunoblotting. Inoculation of mice with 1 of the 3 extracts or the saline solution antigen resulted in marked antibody responses; however, protection against intraperitoneal challenge exposure to P haemolytica was minimal.