The superplastic characteristics of 3-mol%-yttria-stabilized tetragonal-zirconia polycrystals (3Y-TZP) were drastically improved by the combined addition of germanium oxide and other oxides (titanium, magnesium, and calcium), resulting in up to 1000% elongation under optimum conditions. Extensive, work hardening of the codoped compositions for temperatures > 1400 degreesC was observed. Dynamic grain growth was not a sufficient mechanism to explain this anomalous high strain hardening. The appearance of a cubic phase that caused abnormal grain growth during testing may have resulted in increased flow stress, which resulted in exaggerated work hardening.