The relationship of colloid osmotic pressure (COP) to pulmonary edema and mortality in 128 critically ill patients was investigated in our critical care unit, and confirms previously reported observations. The COP in the 86 survivors was 22.0 (+/- 0.4 SEM) mm Hg versus 17.2 (+/- 0.6 SEM) mm Hg in the 42 who died (P less than 0.001). The patients were divided into three groups: 71 with no pulmonary edema, COP of 21.5 (+/- 0.5 SEM) mm Hg; 40 with cardiogenic pulmonary edema, COP of 21.4 (+/- 0.4 SEM) mm Hg; and 17 with noncardiogenic pulmonary edema, COP OF 13.6 (+/- 0.8 SEM) mm Hg. Colloid osmotic pressure was significantly lower in patients with noncardiogenic pulmonary edema (P less than 0.001). In 36 patients in whom pulmonary artery wedge pressures (PWP) were available, a COP-PWP gradient of 4.0 mm Hg or less was always associated with pulmonary edema, while a COP-PWP gradient greater than 4.0 mm Hg was never associated with pulmonary edema. Colloid osmotic pressure is a useful prognostic indicator of pulmonary edema and mortality in the critically ill.