To date no nucleic acid has been found in the purified infectious agent which causes the spongiform encephalopathy known as scrapie. In an attempt to identify a unique scrapie virus-associated messenger RNA in tissues of infected animals, we have synthesized an oligonucleotide probe complementary to the mRNA sequence corresponding to the amino-acid sequence of the prion protein, PrP27–30 (ref. 1). We report here that, with this probe, a complementary DNA clone representing PrP27–30 was obtained from scrapie-infected mouse brain; the DNA sequence of this clone could be translated into a protein that matches exactly the published sequence of PrP27–30. The cDNA clone hybridized to a single 2.4–2.5-kilobase (kb) mRNA from both normal and scrapie-infected brain. Thus, the PrP27–30 mRNA is not uniquely associated with scrapie infectivity, suggesting that PrP27–30 may be a normal component of mouse and hamster brain.