Total cytoplasmic polyadenylated RNA was isolated from the human lymphocyte cell line Wil2 by oligo(dT)-cellulose chromatography. Tritiated complementary DNA (cDNA) was transcribed from the RNA and used as a probe for in situ hybridization to metaphase chromosomes. The majority of G-negative or lightly staining bands were found to be preferential sites of hybridization.