Inverse gas chromatography has been used to measure the thermodynamic interaction between poly(4-hydroxystyrene) (P4HS) and poly(epsilon-caprolactone) (PCL) at 190 degrees C. The retention behaviour of the homopolymers and three blends (0.25, 0.5 and 0.75 P4HS volume fraction) was characterized for 13 probes. The polymer-polymer interaction parameter chi(23) calculated from the Soctt-Flory-Huggins formalism showed an apparent dependence on the probes. The method based on the equation-of-state theory given by Horta et al, and a more simplified method recently proposed by Deshpande were applied to eliminate the influence of the probe on chi(23). The results of these methods were closely similar to the one obtained by melting-point depression of the PCL in the binary blends. Negative values of chi(23) confirm the miscibility of the system. A blend composition dependence of chi(23) has been found, leading to more miscible blends when the PCL content increases. This behaviour was related to the differences in the surface-to-volume ratio of both polymers.