In this protocol, sample and competitor RNAs are reverse transcribed (separately) in a pilot experiment. A constant amount of sample RT product is then combined with a 2-logserial dilution of competitor RT product for PCR. Procedure provides an approximate copy number for the sample, which is then fine-tuned by repeating the experiment with a series of twofold dilutions of competitor. The experiment includes controls for sample-to-sample variations in RT efficiency.