Quantitative measurements of RT reactions performed with five commercial systems. Amounts equal to 1/10 (2 μl) of the undiluted RT samples were quantified by qPCR (two-step qRT-PCR). Data are reported as the number of amplifiable cDNA copies in RT reactions spiked with 1 fg (A) or 1 pg (B) EGFP-template mRNA. All RT systems were tested and all results are reported, except for the Omniscript system in the presence of low-abundance transcript (A), which was undetectable. All RT reactions were performed and quantified in triplicate for each amount of background RNA ranging from 10 ng to 2 μg. Absolute values of EGFP copy number are deduced from a standard curve (Supplementary Table S1a) established with a purified EGFP DNA fragment (Methods). Statistical analysis is presented in Supplementary Table S3. *Different from other RT systems within a different background RNA quantity (P < 0.05; Supplementary Table S3).