Critical miscibility phenomena in binary blends of chlorinated polyethylenes (CPEs) with a wide range of degree of chlorination (37 to 69 wt 970 CI) were studied by measuring the glass transition behavior. At a given temperature the miscibility of the blends was principally dependent on the difference in chlorine content between the two component CPEs and also on the mean degree of chlorination. The miscibility of these systems at 150°C was maximal around an average mole fraction chlorination, β, of 0.5. The systems displayed upper critical solution temperatures when β was below 0.5, while lower critical solution temperatures were observed when β | was above 0.5. At a given β, | the consolute points converged as the difference in chlorine content of the blend constituents increased. It appears that this double consolute point temperature decreases with increasing average degree of chlorination. A more refined analysis, taking into account the possible presence of CCl2units and the microstructure of the CPEs, is also presented.