The Value of pH, PO2 and PCO2 Determinations in the Differential Diagnosis of Pleural Effusions In this experiment we tried to emphasize the Importance of detecting pH, P02, PC02 values in pleural fluid. The pH. P02 and PC02 values were examined in 13 malignant effusions, 21 tubercu¬ios's, 6 congestive heart failure, 2 parapneumonic effusions, 1 chronic nephritis, 1 lupus erithematosus and 1 lung infarction. In patients who had empyema the pleural fluid pH was statistically lower and PC02 was higher than other causes of pleural effusion.