Cu2+ accumulation by S. cerevisiae resulted in rapid release of 70% of cellular K+, followed by a slower release of approximately 60% of cellular Mg2+, but little loss of Ca2+. Co2+ was accumulated in smaller quantities and caused a smaller loss of physiological cations than either Cu2+ or Cd2+. Mg2+ release during copper accumulation was maximal at pH 6. Mg2+ release during Cu2+ accumulation increased with temperature and salinity of the suspension.