 Patients enrolled in the study will undergo daily measurements of plasma CRP Dry Chemistry - Johnsons Johnsons and PCT BRAHMS PCT VIDAS levels up to stopping antibiotic therapy, every 48hr for two measurements in patients remaining in the ICU, and then, every 5 days.Patients will be followed up 28 days, or until death or hospital transference, which comes first. PCT and CRP results will be released in sealed envelopes. During the study period, only the results corresponding to the patient randomization group will be open; i.e., CRP for CRP group patients and PCT for PCT group patients. 