Solutions of poly(2-ethyl-2-oxazoline), PEOX, and poly(2-methyl-2-oxazoline), PMOX, in water and PEOX solutions in several alcohols were characterized by light scattering. The second virial coefficients in water were found to decrease with increasing temperature, reflecting lower critical solution behaviour due to hydrogen bonding. This resulted in negative values of the excess enthalpy DELTAh(E) and entropy of dilution DELTAs(E) for PEOX and PMOX in water. The magnitudes of DELTAh(E) and DELTAs(E) were higher for PMOX than for PEOX. The magnitudes of DELTAh(E) and DELTAs(E) for PEOX increased with molecular weight. The second virial coefficients of PEOX in water were systematically lower than in ethanol, isopropanol and n-butanol.