Changes in cardiopulmonary function and platelet count were determined in 22 dogs of various breeds that underwent total hip replacement with cemented femoral prostheses. In 11 dogs (group I) polymethylmethacrylate (PMMA) was inserted without venting the reamed and lavaged femoral canal. In a second group of 11 dogs (group II) a urethral catheter (ID: approximately 2.7 mm) was placed into the medullary cavity before the insertion of PMMA. The application of PMMA resulted in a decrease in end-tidal carbon dioxide tension (PETCO2) until 5 minutes after insertion of bone cement. Increases in arterial to end-tidal pCO2 gradient [P(a-ET)CO2] and physiological dead space (VD/VT) were recorded between 2 minutes before and 5 minutes after insertion of PMMA in 12 dogs. A significant decrease in platelet count occurred in both groups of dogs. Decreases in arterial pO2 (PaO2), arterial/alveolar oxygen tension ratio (PaO2/PAO2), and percent O2 saturation of hemoglobin in arterial blood (SaO2) were not statistically significant. No significant differences could be detected between data obtained from both groups of dogs. An increase in femoral intramedullary pressure caused by the insertion of PMMA and subsequent pulmonary microembolism by medullary contents has been considered the most likely cause for changes in pulmonary function. The lack of statistically significant differences in cardiopulmonary variables and platelet count between the two groups of dogs could have been related to inefficient pressure reduction by the method used.