Forty-two patients with proven intra-abdominal sepsis were studied in a prospective clinical trial. The following parameters were evaluated: (1) Nine parameters on admission: age, sex, obesity, malnutrition, history of cardiac, respiratory or renal disease, diabetes mellitus and malignant neoplasia. Four of these parameters had a prognostic value (p less than 0.05): age 65 years, diabetes mellitus and cardiac disease. (2) Thirty parameters representing the functional status of six organic systems during sepsis: respiratory, cardiovascular, nervous, kidneys, blood coagulation, liver. Six of these parameters had a prognostic values: PEEP 0-10 cm H2O to keep PaO2 greater than 60 mmHg (p less than 0.001), serum creatinine greater than 3.6 mg/dl (p less than 0.01), prothrombin time greater than 15'' or platelet count less than 100,000/mm3 (p less than 0.001), need of vasoconstrictive drug to keep arterial pressure greater than 100 mmHg (p less than 0.001), bilirubin greater than 3 mg/dl (p less than 0.01) and mental confusion. The combination of these ten statistically significant prognostic criteria for each patient showed that the mortality was 0 with 0-2 criteria, 36% with 3-5 criteria, 94% with 6-8 criteria and 100% with 8-10 criteria. Patients with more than five of these criteria had a significant higher mortality risk (p less than 0.001).