Polymerase chain reaction (PCR) has been applied to the amplification of long DNA fragments from a variety of sources, including genomic, mitochondrial, and viral DNAs (1-5). We have adapted the concept of long PCR technology to reverse-transcription (RT) PCR (6). Here, we describe the parameters critical in producing RT-PCR products of up to 20 kbp. The nature of RT-PCR requires the synthesis of a cDNA by RT prior to its amplification in the PCR reaction. Thus, we focus on the three steps of RT-PCR: the preparation and requirements of the RNA template, the reverse transcription reaction, and the amplification of the cDNA by PCR.