This report describes the length of the entire vena cava in Japanese subjects. This length is important for the use of the new intravenous oxygenator (IVOX). The IVOX is used as an intravascular artificial lung. Situated in the vena caval system, IVOX extends from the upper end of the superior vena cava via the right atrium to the lower end of the inferior vena cava. It was first reported by Mortensen (1987) and has been used clinically in the United States and Europe. The IVOX has four sizes, which range in length from 30 to 40 cm. When using the IVOX for Japanese subjects, a vena cava size that accommodates the IVOX should be chosen. We measured the length of the entire vena cava in 34 cases at postmortem examination. These lengths varied from 30 to 46 cm. The calculated average caval distance was 37 cm with a standard deviation of * 4 cm. Among three corporal indexes of weight, height, and body surface area, the most significant statistical correlation was between vena cava length and patient height. The regression equation for this is as follows: Y = -13.0 + 0.31 x X, where Y is predicted length of the vena cava (cm), and X is patient height (cm). This finding should serve as a relatively simple means for calculating the length of the entire vena cava, and it should be useful in clinical practice with the IVOX in Japan.