The 5'-flanking region of the Chinese hamster ovary metallothionein-I gene (MT-I) was isolated and sequenced. This region contains several cis-regulatory sequences, including metal-responsive element (MRE), AP1-binding site, Sp1-binding site and glucocorticoid-responsive element (GRE). These elements are located within 250 bases upstream of the transcription initiation site, as determined by primer extension. This region was fused with a reporter gene that could be activated by the challenge of cadmium only when the MREs were present. Thus, the isolated DNA is the promoter region of the CHO MT-I gene.