A prospective study of 126 surgical patients from two institutions was undertaken to assess the impact of pulmonary artery catheterization in surgical intensive care units. Before catheterization, surgical residents were asked to predict pulmonary artery wedge pressure, cardiac output, systemic vascular resistance, and plan of therapy. After catheterization, each chart was reviewed by a panel of intensive care specialists and a general surgeon. Correct classification for the hemodynamic variables ranged from 47% to 55%. Catheterization results prompted a major change in therapy in 50% of patients. The data suggest that hemodynamic variables obtained from pulmonary artery catheterization improve the accuracy of bedside evaluation and lead to alteration in therapy, particularly in patients whose pulmonary artery wedge pressure predictions were poor.