biomarker is defined as a molecular signature found in blood, other body fluids, or tissues that reflects a normal biologic process, pathogenic process or pharmacologic process to a therapeutic intervention, a biomarker can be used to measure the risk for a disease, the progress of a disease or how well the body responds to a treatment for a disease or condition. The biomarkers explained in this essay are biomarkers of cardiac, acute kidney injury, sepsis, chronic obstructive pulmonary disease, type 2 diabetes mellitus, and stress. Cardiac biomarkers play an important role in providing additional information for differential diagnosis in the ICU. This additional information, depending on the biomarker(s) used, may include the presence or absence of cardic disease, cardiac injury, atheroscleortic plaque, or pulmonary embolism. While most information could be obtained from detailed clinical investigations such as echocardiography, angiography and other haemodynamic assessments, the biomarker approach provides quick information and adds value to the diagnostic process. So, a number of cardiac biomarkers are now commonly used in the ICU; in particular, cTn, CRP, and CK-MB. cTn is known to be increased in intensive care patients, and are not confined to patients with cardiac injury or acute coronary syndromes but because of its high sensitivity and specificity for the heart, cTnI is appropriate marker for the diagnosis of perioperative myocardial infarction. Although CRP has been used as a cardiac marker in the emergency or cardiology settings, it is not normally used as a cardiac biomarker in the ICU. CRP is used as an acute phase inflammatory marker to assist the diagnosis of infection. BNP is also a promising biomarker for use in the ICU, but its application is confined mainly to screening purposes. Applications in the area of differential diagnosis, guiding treatment as well as prognosis are still developing. The traditional clinical biomarkers for the detection fo AKI are creatinine, urea, and urine output. All have serious limitations as early detectors of AKI. Because of this limitation, innovative technologies such as functional genomics and proteomics have facilitated the detectionof several potential earlier biomarkers of AKI. Some of the most promising biomarkers include Neutrophil Gelatinase-Associated Lipocalin (NGAL), Cystatin C (CyC), and Liver-type Fatty Acid Binding Protein (L-FABP), which have superior sensitivity and detect AKI earlier than serum creatinine, enhancing the abiology to demonstrate benefits and to justify the implementation of therapies or kidney protective techniques. Biomarkers have an important role in diagnosis of sepsis, because they can indicate the presence or absence or severity of sepsis, and can differentiate bacterial from viral and fungal infection, and systemic sepsis from local infection. Also, they have roles in prognostication, guiding antibiotic therapy, evaluating the response to therapy and recovery from sepsis. Sepsis has large numbers of biomarkers which were related to the very complex pathophysiology of sepsis, which invovles many mediators of inflammation, but also other pathophysiological mechanisms. Coagulation, complement, contact system activation, inflammation, and apoptosis are all involved in the sepsis process, and separate markers for each (part of each) system have been proposed.