Abstract: The BUMI tag is an invention which allows different species of mRNAs from different samples to be quantitatively measured at the first strand cDNA generation step, and is not affected by variations in amplification efficiency of different species of molecules, regardless of amplification method. It consists of a blend of defined nucleotides which comprise the bar-coding portion of the tag along with a set of randomly synthesized nucleotides which comprise the UMI (universal marker indicator) portion of the tag. This blend of Barcode and UMI parts comprises the BUMI tag. The two are interspersed so that the fixed nucleotides of the barcode do not form a contiguous region which might cause biases between different barcodes due to undesired complementarity between the barcode and amplification primers/adaptors.