AbstractÐThe speci®c volumes and viscosities of the Ni±Zr liquid alloys as a function of temperature are determined by employing a digitizing technique and numerical analysis methods applied to the optical images of the electrostatically levitated liquid alloys. The results show that the speci®c volume of the NiZr 2 alloy is signi®cantly smaller than that of an ideal mixture of the constituent metals, thereby indicating the presence of the associated species in the form of NiZr 2 . The presence of NiZr 2 species can account for the observed properties; the speci®c volume anomaly above the melting point under a moderate cooling rate and a relatively small undercooling level prior to crystallization. The results also show that the viscosities of the compound forming alloys are larger than those of the eutectic alloys, thereby indicating the presence of the NiZr and NiZr 2 species. The associated species are stable and exist at temperatures well above their melting points. It is concluded that a small speci®c volume or a large viscosity resulting from the presence of the associated species primarily facilitates the glass formation of the Ni±Zr alloys by slowing down the growth of the crystalline phases.