Chronic kidney disease (CKD) is frequently associated with a progressive decrease in the glomerular filtration rate, which leads to endstage renal disease (ESRD). Heart failure (HF) is a complex syndrome rather than a primary diagnosis, and considered as the endpoint of all cardiovascular disorders. It is the leading cause of death among the cardiovascular diseases in patients with CKD and ESRD. There is some interaction between the heart and kidney (the so-called "cardiorenal syndrome"), and HF patients with the complication of CKD or ESRD show a worse prognosis. Thus, early diagnosis and aggressive management of HF are needed in patients with CKD and ESRD. A number of biomarkers appear to have growing clinical importance and are reported for detection and stratification of HF. Although HF and CKD have a close interrelationship, the utility of the biomarkers has not been adequately studied with regard to the relationship with renal dysfunction. This paper reviews of the current evidence about laboratory biomarkers in patients with HF or CKD, emphasizing the emerging cardiac biomarkers (ie, BNPs and cardiac troponins), and the biomarkers of renal injury (ie, cystatin C and neutrophil gelatinase-associated lipocalin). Furthermore, it discusses the potential role of these markers in terms of heart - kidney interactions and their utility in the diagnostic and therapeutic strategies for cardiorenal syndrome.  (Circ J 2010; 74: 1274 - 1282)