BACKGROUND: Systemic inflammatory reaction syndrome (SIRS) describes the systemic inflammatory process and can be seen following a wide variety of insults. This is the leading cause of morbidity and mortality for patients admitted to the ICU. The arterial keton body ratio (AKBR), serum lactate level and the thyroid hormones, thyroid stimulation hormone (TSH), thyroxine (T4), free thyroxine (FT4) and triiodothyronine (T3) deteriorate in critically ill patients with a poor prognosis. The APACHE (Acute Physiology, and Chronic Health Evaluation) III and multiple organ failure (MOF) score have been known as good prognostic predictors in the ICU. The object of this study was to compare the AKBR, lactate and thyroid hormone levels, and the APACHE III and MOF score between the survivors (SV) and nonsurvivors (NSV) and the correlation among the above predictors. METHODS: 35 patients with no known thyroid or liver disease who were admitted to the SICU with the criteria of SIRS were selected. Arterial blood was drawn for the AKBR, and the lactate and thyroid hormones studies. The APACHE III and MOF scorings were done in the first 24 hours of SICU admission. RESULTS: There were no significant difference between SV and NSV except APACHE III (SV: 68.7 24.6, NSV; 92.9 27.6). There were significant correlations between the APACHE III and MOF score (R = 0.688, P<0.01), APACHE III and lactate (R = 0.575, P<0.01), and MOF score and lactate (R =0.483, P<0.01). Thyroid hormones had positive correlations among themselves only. CONCLUSIONS: We conclude that APACHE III is the only good predictor of mortality. The APACHE III, MOF score, and lactate level show good correlations indicating the severity in condition of the ICU patients.