The Flory θ-temperature (Tθ), where the excluded volume of the chain is just balanced by the attractive interactions and the polymer chain assumes its unperturbed dimensions, must be determined before measurements can be made at θ conditions. The most common method of determination is extrapolation of cloud point temperatures to infinite molecular weight. Alternatively, the temperature where the second virial coefficient, A2,vanishes can be determined by light scattering or osmotic measurements. © 1986, American Chemical Society. All rights reserved.