In a cadmium-resistant strain of Saccharomyces cerevisiae, cells are protected against cadmium toxicity by the production of large amounts of cadmium-binding metallothionein, as occurs similarly in a copper-resistant strain. The apoprotein of the metallothionein is encoded by the CUP1 gene on chromosome VIII. The CUP1 gene is present as 8-10 copies in the cadmium-resistant strain a a result of tandem repeat of a 2.0-kb fragment of DNA that includes CUP1, while the wild-type strain contains only a single copy of CUP1. In the cadmium-resistant strain, some evidence for elongation of chromosome VIII with variations in length (maximum to 200 kb) was obtained. However, the elongation was not due to the tandem repeats of the CUP1-containing region.