The initial distribution volume of glucose (IDVG) can be calculated from the arterial plasma glucose level between 3 and 7 min after a bolus intravenous infusion of 5 g glucose. Ishihara and colleagues have investigated the value of IDVG over the past decade. Although IDVG is simple and cheap to measure, there have been several very different proposals regarding what it should be used for. The most interesting and logical correlate is that between IDVG and cardiac output. A recent study showed that it does not matter much whether the calculation of IDVG is based on blood or plasma samples.