MicroRNAs (miRNAs) are small noncoding RNAs (18-25 nucleotides) that regulate gene expression at the posttranscriptional level.Recent studies have demonstrated the presence of miRNAs in the blood circulation.Deregulation of miRNAs in serum or plasma has been associated with many diseases including cancers and cardiovascular diseases,suggesting the possible use of miRNAs as diagnostic biomarkers.However,the detection of the small amount of miRNAs found in serum or plasma requires a method with high sensitivity and accuracy.Therefore,the current study describes polymerase chain reaction (PCR)-based methods for measuring circulating miRNAs.Briefly,the procedure involves four major steps:(1) sample collection and preparation; (2) global miRNAs profiling using quantitative real-time PCR (qRT-PCR); (3) data normalization and analysis; and (4) selection and validation of miRNA biomarkers.In conclusion,qRT-PCR is a promising method for profiling of circulating miRNAs as biomarkers.