The effect of experimental, peracute, porcine pleuropneumonia on arterial blood gases, acid base status, the leukogram, and gross and microscopic lung structure was studied in nine growing pigs (mean weight +/- SD 10.6 +/- 2.0 kg). Pigs were inoculated intranasally with a virulent serotype 5 isolate of Actinobacillus pleuropneumoniae, and all showed signs typical of the disease within four hours. Death occurred in all pigs from 4.5 to 32 hours postinoculation (mean 14 hours). Gross and microscopic changes were typical of porcine pleuropneumonia in all pigs. Changes in the leukogram included a rapid decline in total white cells, segmented neutrophils, lymphocytes, monocytes, and eosinophils. Pigs maintained alveolar ventilation throughout the study as arterial CO2 tension was unchanged; however, arterial O2 tension and pH decreased from (mean +/- SD) 95.2 +/- 5.7 torr and 7.463 +/- 0.018 at baseline to 62.1 +/- 12.3 torr and 7.388 +/- 0.045, respectively, within 90 minutes prior to death. The data showed that in this model of peracute porcine pleuropneumonia, progressive ventilatory failure was not a feature of the disease, and the blood gas values and acid base status were maintained within physiological ranges. The histopathological hematological and physiological findings were consistent with the hypothesis that peracute porcine pleuropneumonia resembles septic shock.