Pathologic dependency of .ovrhdot.VO2 on .ovrhdot.DO2 has been reported in postoperative and septic patients. We studied the influence of an artifact due to calculation of .ovrhdot.VO2 from CO and AV content difference. In 13 postoperative and seven septic patients, the relationships between .ovrhdot.DO2 and c.ovrhdot.VO2 and between .ovrhdot.DO2 and m.ovrhdot.VO2 were analyzed by linear regression. In ten patients, c.ovrhdot.VO2 and .ovrhdot.DO2 were significantly correlated, but in only two of these patients m.ovrhdot.VO2 also correlated with .ovrhdot.DO2. In two patients, there was a significant correlation between m.ovrhdot.VO2 and .ovrhdot.DO2. The main contribution to the correlation and to the slope of the regression line between c.ovrhdot.VO2 and .ovrhdot.DO2 may be due to mathematic coupling of c.ovrhdot.DO2 and .ovrhdot.DO2. With c.ovrhdot.VO2, erroneous conclusions concerning the .ovrhdot.DO2-.ovrhdot.VO2 relationship may be drawn. In four patients, .ovrhdot.VO2 and m.ovrhdot.VO2 were significantly related, reflecting either physiologic coupling or pathologic supply dependency of .ovrhdot.VO2.