Oligo (dT)₁₈ primer is a synthetic single-stranded 18-mer oligonucleotide with 5’- and 3´- ends. Oligo (dT)₁₈ is suitable for use as a primer for first-strand cDNA synthesis with a reverse transcriptase. The primer hybridizes to the poly(A) tail found at the 3´-end of most eukaryotic mRNAs, making them more specific than random hexamers, as they will not transcribe rRNA. Oligo (dT)₁₈ primer is frequently employed when cDNA is used for cloning, cDNA library construction and qPCR.