Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are simple, fast and non-invasive laboratory tests, and are used for the detection or monitoring of patients with suspected inflammatory disease. Selection of ESR or CRP in the processing and / or treatment of a patient depends on the diagnostic value of the test for a given condition or disease. ESR is one of the oldest laboratory tests, in which the speed of the sedimentation depends on the shape and the number of red blood cells and plasma composition. ESR is elevated in some physiological states as in pregnancy, and in a number of pathological conditions it is associated with inflammation, anemia, paraproteinemia, increased concentration of fibrinogen, presence of cold agglutinins. The reference range for ESR varies dependent on age and sex and ranges from • 15 mm / h to • 49 mm / h. The red blood cells in normal conditions repel one another. Sialic acid is on the erythrocyte membrane and protects the cells of accelerated aggregation. In inflammatory conditions proteins of acute response are increasingly synthesized, fibrinogen or immunoglobulins. These proteins inhibit the protective effect of sialic acid on the surface of red blood cells, so they quickly settle down. To determine the erythrocyte sedimentation speed International Council for Standardization in Haematology (ICSH) recommends a method by Westergren, which measures the speed of sedimentation of erythrocytes in a standardized graduated pipette in a given time (1 hour) at room temperature. In recent years new, automated methods were developed of which some are modifications of classical Westergren method. Most methods for automated determination of sedimentation uses analyzers to apply microphotometer with infrared ray to determine the optical density of the sample. The methods are simple and fast, but they are not standardized. CRP is the most important marker of acute inflammatory response, it is more sensitive than ESR, and it is in good correlation with the severity and extent of inflammation. Despite the opinion that the value changes of ESR and CRP have similar pathophysiological basis in the background, there are differences in values between the two analytes for the same disease Among the acute phase proteins that can easily be measured in the laboratory, CRP is one of the more sensitive tests with fast response. ESR is not specific for the acute phase inflammatory response and is affected by hematocrit, red cell size and shape Recommended methods for the determination of CRP are unmarked or direct techniques, npr. immunonephelometry, immunoturbidimetry and radial immunodiffusion. In the laboratory diagnostics knowledge of the features of methods for determining the SE and CPR means a selection of a suitable sample and method, and the knowledge of the limitations of the method.