We have identified by differential plaque hybridization, human cDNA clones encoding a member of a heat-shock protein family (hsp 90 alpha) in the cDNA library of Adenovirus Type 12 E1A transfected HeLa cells. The complete nucleotide sequence of one of the clones (pHB76-114A) was identified. The sequence of 2912 base pairs had a single reading frame with a coding potential for an 84,672-Da protein. The amino acid sequence was highly homologous, but not identical, to that of the human hsp 90 alpha gene isolated from human peripheral blood lymphocytes [M. Yamazaki, K. Akaogi, T. Miwa, T. Imai, E. Soeda and K. Yokoyama, Nucleic Acids Res., 17, 7108 1989)]. This cDNA hybridized with RNA species which increased 5- to 20-fold upon heat shock and more than 5-fold in the differentiation stage of human Tera 2 cells.