In dogs, the venous blood from the prostate gland was observed under X-ray fluoroscopy to drain into the vertebral venous system under conditions of abdominal compression, the addition of various intraabdominal pressures, and occlusion of the inferior vena cava by a balloon catheter. Pressure in the inferior vena cava and abdominal cavity were measured simultaneously. The venous blood draining from the prostate gland started to flow from the inferior vena cava into the vertebral veins at more than 25 mmHg of intraabdominal pressure with the animal in the supine position. The average pressure of the inferior vena cava draining into the vertebral veins was 12.8 +/- 1.3 mmHg in the supine position and 21.1 +/- 2.7 mmHg in the standing position. The average intraabdominal pressures were 35.5 +/- 3.9 mmHg and 30.1 +/- 2.8 mmHg, respectively. Under conditions of abdominal compression and balloon occlusion of the inferior vena cava, the materials flowed into the vertebral venous system from various routes, such as the internal iliac vein, common iliac vein, and inferior vena cava. It was suggested that the inferior vena caval blood easily enters the vertebral venous system in the standing position by adding high intraabdominal pressure, and that the vertebral venous system may be useful for experimental study of drug administration in bone metastasis of prostate cancer.