Tracer diffusion of ⁶⁰Co and ⁶³Ni in the amorphous alloy NiZr near the equiatomic composition has been measured in the temperature range between 486 and 641 K using the ion-beam sputter-sectioning technique for serial sectioning. The temperature dependence for the diffusivities of Co and Ni in a-NiZr exhibit Arrhenius behavior; these can be expressed as follows: D^∗_co = 3.6 × 10⁻⁷ exp [− (135 ± 14) kJ mol⁻¹ /RT] m²/s and D^∗_Ni = 1.7 × 10⁻⁷ exp [− (140 ± 9) kJ mol⁻¹ /RT] m²/s. The values of D^∗_Ni are in good agreement with those measured by the Rutherford backscattering technique. The measured diffusivities were independent of time, indicating that no relaxation took place during diffusion.