We have constructed libraries of recombinant DNA plasmids containing sequences complementary to polyadenylated RNA from a variety of human midtrimester fetal tissues. The bacterial colonies containing these plasmids have been grown and replicated on nitrocellulose filters in a manner that facilitates permanent storage, rapid screening, and transportability to other laboratories. We screened a portion of the library for the presence of repetitive sequences and found that approximately 20% of the clones contain repetitive sequences. We have also shown that some clones contain nonrepetitive sequences. Pools of recombinant cDNA-containing plasmids devoid of repetitive sequences have been constructed to permit the chromosomal localization of a variety of actively transcribed sequences. The construction of such large, tissue-specific clone banks should facilitate the direct isolation, mapping, and characterization of normal and abnormal human genes.