The rheology of a highly filled thermoplastic paste employed in a novel continuous casting process was investigated across the melt-mushy zone temperature transition. The paste comprises of an ultrafine (or nano-particulate) zinc oxide powder (d(1,0)=85 nm, 50vol%) and a continuous phase consisting of a blend of organic waxes with an onset of solidification around 54 degrees C. Data were collected over nine decades of shear rate, using controlled strain and controlled stress devices, steady shear and oscillatory modes, rotational rheometry, and capillary rheometry using the multi-pass technique. The melt rheology could be described using a Carreau-type constitutive model, with strong evidence of a low shear rate viscosity plateau and a possible high shear rate viscosity plateau, with a transition between the two described by a highly shear-thinning power-law region. Nearer the solidification temperature the material exhibited strong pseudo-plastic behaviour, and capillary flow appears to be determined by pressure-dependent slip behaviour. (C) 2007 Elsevier Ltd. All rights reserved.