Certain heavy metal ions such as copper and zinc serve as essential cofactors of many enzymes, but are toxic at high concentrations. Thus, intracellular levels have to be subtly balanced. P-type ATPases of the P1B-subclass play a major role in metal homeostasis. The thermoacidophile Sulfolobus solfataricus possesses two P1B-ATPases named CopA and CopB. Both enzymes are present in cells grown in copper-depleted medium and are accumulated upon increase of the external copper concentration. We studied the physiological roles of both ATPases by disrupting genes copA and copB. Neither of them affected the sensitivity of S. solfataricus to reactive oxygen species, nor was a strict prerequisite to the biosynthesis of the copper protein cytochrome oxidase. Deletion mutant analysis demonstrated that CopA is an effective copper pump at low and high copper concentrations. CopB appeared to be a low affinity copper export ATPase becoming relevant only if the media copper concentration is exceedingly high. CopA and CopB thus act as resistance factors to copper ions at overlapping concentrations. Moreover, growth tests on solid media indicated both ATPases also being involved in resistance to silver.