Poly(A)+ RNA enriched in alpha 2-macroglobulin (alpha 2M) mRNA isolated from livers of rats 18 h after injection of turpentine was used for the synthesis of double-stranded cDNA. The double-stranded cDNA was inserted into the PstI site of the plasmid pBR322 by oligo(dG)-oligo(dC)-tailing technique. Clones containing sequences complementary to alpha 2M mRNA were selected by differential colony hybridization using 32P-labeled poly(A)+ RNA and [32P]cDNA from livers of control and turpentine-treated rats and subsequent hybrid-selected translation. The isolated p alpha 2M1 clone had an insert of 657 base pairs. DNA sequence analysis revealed a homology of about 80% to human alpha 2M. Northern analysis showed that the alpha 2M mRNA from rat liver is about 5600 bases in length. The alpha 2M cDNA was used to measure the in vitro transcription of the alpha 2M gene in isolated nuclei. A 4-fold increase in alpha 2M gene activity was found 14 h after turpentine administration. We conclude that alpha 2M transcription is induced during inflammation.