The thermodynamic absorption parameters of a series of disazo dyes derived from paminophenol and 4-aminobenzoic acid on polyester and nylon 6 substrates are described. It was found that the dyes generally have higher affinities for the polyester fibre than for the nylon 6 fibre. The values of Δm0, ΔH0, and ΔS0 in the two dye-fibre systems suggest that the hydrogen bonding mechanism is operative in the dye-fibre binding forces. The very high values of correlation coefficients showed that the rate curves fit the experimental data perfectly. The results of the study also showed that certain intrinsic properties such as planarity and molecular volume could be more useful in interpreting activation energy of diffusion data.