Right atrial pressure (RAP) can be used as a guide to fluid therapy in critical care settings. RAP and pulmonary capillary wedge pressure (WP) were measured in 27 septic patients without cardiac disease and on mechanical ventilation. An r of .61 was obtained with a regression line defined by the equation WP = 7.38 + (0.53 x RAP) +/- 3.15. However, a large SD of data points can invalidate the clinical usefulness of this equation. The reliability of various RAP interval values in predicting optimal WP was then studied in these patients. We concluded that RAP values less than or equal to 5 mm Hg were highly specific (97%) in predicting low or normal WP (less than or equal to 12 mm Hg).