Through preliminary plate tests, Kluyveromyces marxianus was found to be much more resistant to toxic heavy metals compared to a CUP1R strain of Saccharomyces cerevisiae. Specific growth rate and maximum dry weights affected by increasing metal concentrations were determined to obtain precise patterns of resistance. Metal biosorption was also monitored during the course of growth in synthetic media containing respective metals at 0.5 mM final concentration. Although Zn- and Co-binding was negligible, as much as 90% of silver, 60% of copper, and 65% of cadmium were found to be absorbed by the end of active growth. Analysis of the protein profiles of S. cerevisiae and K. marxianus on metal exposure suggested constitutive production of metallothionein in K. marxianus. Furthermore, a smaller protein synthesized by K. marxianus on induction by silver or cadmium accounts for the high resistance of the organism to these metals.