Despite the advances and a wide range of studies conducted, sepsis is one of the most frequent causes of death in patients with critical health condition. Early diagnosis, rapid and effective treatment are extremely important. Use of procalcitonin (PCT) for this purpose has become widespread and notable recently. Procalcitonin is an important test as “point-of-care testing (POCT)” just like C-reactive protein (CRP). Procalcitonin is the prohormone of calcitonin. It is released from the parenchymal cells of the liver, kidneys and muscles, and in response to bacterial toxins, it is released from the adipocytes. As a response to bacterial infection, the serum procalcitonin level may increase by 5000-fold within 2-4 hours. C- reactive protein is synthesized in the liver as a result of interleukin-6 (IL-6) trigger due to tissue injury, inflammation and/or infections. The aim of our study was to emphasize the importance of PCT as an indicator in patients suspicious of sepsis in the early period. A total of 66 patients with critical situation were included in the study conducted at the İnönü University Medical Faculty Turgut Özal Medical Center Investigation Hospital between February 2007 and August 2008. These patients were appropriate for the diagnostic criteria of systemic inflammatory response syndrome (SIRS). Appropriate antibiotiotherapy was begun for the patients. The PCT and CRP levels were investigated on the first day after having been included in the study, and on the third and seventh days. The mean C-reactive protein levels were 132.41, 108.39 and 83.47 mg/l on the 1, 3rd and 7th days, respectively. The minimum level of procalcitonin was 0.095 ng/ml on the first day, and the maximum level was 316.054 ng/ml. The minimum/maximum levels were 0.091 and 306.043 ng/ml on the 3rd day, and 0.081 and 12.15136 ng/ml on the 7th days, respectively. No statistically significant difference was observed betweern the serum procalcitonin levels on the 1st and the 3rd days ( p<0.229), whereas a significant difference was observed between its levels between the 1st and the 7th days (p<0.002). Likewise, the difference between the 3rd and the 7th days was statistically significant (p<0.005). C-reactive protein levels revelaed a significant difference between the 1st and the 7th days (p<0.013) and between the 3rd and the 7th days (p<0.010). The Wilcoxon Signed test was used to investigate statistical significance. The diagnostic value of procalcitonin has been widely used in septic patients. Although conflicting results have been obtained in different studies, despite the fact that some studies have not found PCT supportive for the diagnosis of sepsis, we believe that PCT is an appropriate and important indicator in the early diagnosis and follow-up of sepsis as CRP