Polymer complexes of poly(N-isopropylacrylamide) with poly(acrylic acid) and poly(methacrylic acid) have been isolated as a consequence of their mutual precipitation in aqueous solution. Their composition can be represented, in most cases, by simple molar ratios of the interacting groups. The glass transition temperature (T-g) of the complexes is higher than that of their components. Blends of these polymers cast from clear methanol solutions have also been prepared. Again, T-g values of the blends are higher than the component ones, but now a dependence on the composition of the mixture is observed. The thermal behaviour of complexes and blends has also been studied.