The authors describe a method for amplifying heterogeneous populations of RNA from limited quantities of cDNA, which is particularly useful for studying neural gene expression. They use a synthetic oligonucleotide containing the T7 RNA polymerase promoter sequence to prime cDNA synthesis, followed by T7 RNA polymerase to generate amplified antisense RNA (aRNA). This method has achieved up to 80-fold molar amplification from nanogram quantities of cDNA. The amplified aRNA retains the size distribution and sequence heterogeneity of the original cDNA, as demonstrated by Southern and Northern blot analysis. Specific messages for moderate-abundance mRNAs, such as actin and guanine nucleotide-binding protein (G-protein) α subunits, have been detected in the amplified material. The technique is also applied to detect sequences in aRNA derived from single cerebellar tissue sections and individual Purkinje cells. The authors discuss the potential applications of this method in constructing cDNA libraries, producing specific ribonucleotide probes, and facilitating studies of neural gene expression.The authors describe a method for amplifying heterogeneous populations of RNA from limited quantities of cDNA, which is particularly useful for studying neural gene expression. They use a synthetic oligonucleotide containing the T7 RNA polymerase promoter sequence to prime cDNA synthesis, followed by T7 RNA polymerase to generate amplified antisense RNA (aRNA). This method has achieved up to 80-fold molar amplification from nanogram quantities of cDNA. The amplified aRNA retains the size distribution and sequence heterogeneity of the original cDNA, as demonstrated by Southern and Northern blot analysis. Specific messages for moderate-abundance mRNAs, such as actin and guanine nucleotide-binding protein (G-protein) α subunits, have been detected in the amplified material. The technique is also applied to detect sequences in aRNA derived from single cerebellar tissue sections and individual Purkinje cells. The authors discuss the potential applications of this method in constructing cDNA libraries, producing specific ribonucleotide probes, and facilitating studies of neural gene expression.