A method for isolating mRNAs as cDNAs employs a polymerase amplification method using at least two oligodeoxynucleotide primers. In one approach, the first primer contains sequence capable of hybridizing to a site immediately upstream of the first A ribonucleotide of the mRNA's polyA tail and the second primer contains arbitrary sequence. In another approach, the first primer contains sequence capable of hybridizing to a site including the mRNA's polyA signal sequence and the second primer contains arbitrary sequence. In another approach, the first primer contains arbitrary sequence and the second primer contains sequence capable of hybridizing to a site including the Kozak sequence. In another approach, the first primer contains a sequence that is substantially complementary to the sequence of a mRNA having a known sequence and the second primer contains arbitrary sequence. In another approach, the first primer contains arbitrary sequence and the second primer contains sequence that is substantially identical to the sequence of a mRNA having a known sequence. The first primer is used as a primer for reverse transcription of the mRNA and the resultant cDNA is amplified with a polymerase using both the first and second primers as a primer set.