1. Using haploid strains which had never been exposed to copper medium but had three different levels of copper resistance, the following facts were observed:
a. Hybrids showed the same resistant level as the more resistant one of the parents.
b. The most resistant haploid strain grew more slowly than other strains in the non-copper medium.
c. Sensitive strains accumulated more copper in cells than the strains of higher resistance.
d. The most sensitive strain was more sensitive to p-chloromercuribenzoic acid and arsenite than more resistant strains.
2. In the copper resistant strain obtained by “training”. copper seems to be accumulated as sulfide.
3. For the “untrained” strains and for the early growth phase of “trained” strains, thiol-compounds are suspected to detoxify copper in the cell.