Rapid amplification of complementary DNA (cDNA) ends (RACE) is a powerful technique for obtaining the ends of cDNAs when only partial sequences are available. In essence, an adaptor with a defined sequence is attached to one end of the cDNA; then, the region between the adaptor and the known sequences is amplified by polymerase chain reaction (PCR). Since the initial publication in 1988 (1), RACE has greatly facilitated the cloning of new genes. Currently, RACE remains the most effective method of cloning cDNAs ends. It is especially useful in the studies of temporal and spatial regulation of transcription initiation and differential splicing of mRNA. The methods described in this chapter are quite simple and efficient. A linker at the 3′ end and an adaptor at the 5′ end are added to the first strand of cDNA during reverse transcription; amplification of virtually any transcript to either end can then make use of this same pool of cDNAs. In addition to being simple, the efficiency of 5′-RACE is dramatically increased because the adaptor is added only to full-length cDNAs.