Methods are described for obtaining comprehensive flow curves for thermoplastic melts and other viscoelastic liquids at temperatures up to 300° C, using as little as 0.1 to 0.5 g of material, where hitherto 10 to 20 g have been required. Information can also be obtained on elasticity, thermal degradation and flow defects. Such results are important in evaluating the processability of a new polymer at a very early stage in its development. Measurements of viscosity ranging from 10² to 10⁷ poises have been made within the stress range 2 × 10³ to 10⁷ dyn cm^-2; shear moduli of many polymers have been measured and the values all lie in the range 2 × 10⁴ to 2 × 10⁵ dyn cm^-2.