In order to evaluate the relationship among the changes of colloid oncotic pressure (COP), hemodynamic and respiratory recovery after open heart surgery, cardiac index (CI), pulmonary capillary wedge pressure (PCWP), (A-a)DO2, urine output and COP were measured in 33 patients during 48 hours after the cardio-pulmonary bypass (CPB). The patients were divided into three groups according to COP values at 3 and 24 hours after CPB. Twenty three patients whose COP values were normal (COP greater than or equal to 19 mmHg) at 3 hours after CPB maintained stable hemodynamic and respiratory status. Cardio-respiratory status were deteriorated in the 6 patients whose COP values were below normal both 3 and 24 hours after CPB. On the other hand, 4 patients with normal (A-a)DO2 and low COP values at 3 hours after CPB demonstrated rapid recovery of COP values and improvement of cardiac function. It is concluded that the patients with both cardiac and respiratory dysfunction have low COP values during 48 hours after CPB, but the patients with normal (A-a)DO2 and low COP at 3 hours after CPB demonstrate the recovery of COP values with rapid improvement of cardiac function until 24 hours after open heart surgery.