High quality total RNA is used as starting material to obtain labeled cRNA. In the first step, single stranded cDNA is synthesized by reverse transcription using the poly (A) RNA present in the starting total RNA sample. Single stranded cDNA is then converted into double stranded cDNA and purified using the Illumina TotalPrep RNA Amplification Kit. An in vitro transcription (IVT) reaction is then carried out overnight in the presence of biotinylated UTP and CTP to produce biotin-labeled cRNA from the double stranded cDNA. The cRNA from the IVT reaction is purified using the same Amplification Kit. Due to the high cost of cDNA and cRNA synthesis reactions, we use very strict quality control measures during the target preparation procedures.