A 5.1 kb plasmid, pCDR1, which conferred cadmium resistance on Escherichia coli C600, was obtained during the cloning of the cadmium resistance gene from pGU100 harbored by cadmium-resistant Pseudomonas putida GAM-1. pCDR1 was constructed with pBR322 as vector and an about 800 bp inserted fragment. The nucleotide sequence revealed that the inserted DNA fragment was IS1. The cadmium resistance of this transformant was maintained even though the plasmid was cured. Southern analysis showed that the mobility of one band was changed, indicating that a chromosomal rearrangement occurred in the cadmium-resistant strain.