In 175 patients with ascites due to 19 different pathologic conditions, the glucose contents of ascitic fluid and blood were estimated. In patients with ascites produced by portal hypertension or hypoproteinemia, the glucose values were higher in ascitic fluid than in blood. In patients with peritoneal affections, the glucose levels were mostly equal to or lower than those in blood. It is concluded that the determination of blood glucose/ascitic fluid glucose ratio is useful for differentiating ascites due to venous hypertension or hypoproteinemia from ascites due to a peritoneal affection.