The effects of differential centrifugation, density gradient centrifugation, freeze-thawing, and chemical lysis on the morphology of P. multocida from the blood of infected turkeys were examined by electron microscopy. The internal ultrastructure of turkey-grown cells was different from that observed previously for broth-grown P. multocida. Freeze-thawing of bacterial suspensions in sucrose resulted in partial lysis revealing bacteria in different phases of degradation. Complete lysis (but not solubilization) was effected by treatment with EDTA, lysozyme, and Triton X-100. Centrifuged lysate pellets consisted of vesicles, ranging in size from 0.05-1.0 um, that had a characteristic trilaminar membranous appearance. Various treatments on the lysate of turkey-grown Pasteurella multocida were performed to determine the nature of the cross-protection factor (CPF). No cross-protection was produced with pepsin treated lysates. Moderate cross-protection was produced with trypsin treated lysates and cross-protection was unaffected by heating the lysate at 56(DEGREES)C for 1 hour. When the lysate was centrifuged for 1 hour at 100,000 x g, CPF was found in both the supernatant and pellet fractions indicating that the CPF was polydispersed. After sucrose density gradient centrifugation, more CPF was found in the top 15-20% and bottom 50-60% bands than in the middle 30-40% band. The lytic treatment released 84.2% of the cell protein into solution and although the pellet and bottom density gradient fraction had a disproportionally small amount of protein, they had CPF equal in immunizing capacity to the whole lysate and soluble portions of the whole lysate. The effects of 9 membrane solubilizers on pelleted turkey-grown lysate were examined in an effort to release additional protein that may contain the CPF. Soluble vaccines prepared from the lysate supernatant and solubilized lysate pellet material produced varying degrees of cross-protection to a heterologous serotype challenge. Vaccines prepared from solutions containing the most protein solubilized from the pellet did not cross-protect the best. Only two preparations, the KSCN and SLS soluble vaccines, had immunizing capabilities equal to the whole lysate from turkey-grown P. multocida.