Changes in the Lifshitz-van der Waals, gammaLWS, electron donor, gamma-S, and electron acceptor, gamma+S, surface free energy components of leacril fabric due to the adsorption of N-cetylpyridinium chloride (N-CP-Cl) were determined by the thin-layer wicking technique. It was found that the treatment of leacril with different amounts of N-CP-Cl practically does not change the value of the gammaLWS component. The treatments reduce the gamma+S component practically to zero, and a very sharp decrease of gamma-S (from 60.5 to 35.8 mJ/m2) was observed as the leacril was treated with increasing amounts of the above surfactant. It is concluded that the adsorption of N-CP-Cl on leacril takes place by means of electrostatic attractions between the quaternary ammonium group of N-CP and both the sulfonate and the sulfate groups of leacril. These groups could impart hydrophilicity to the surface of the leacril and hence acid-base interactions between the molecules of the surfactant and the surface of the fabric could explain the interactions between the N-CP-Cl and the leacril. The decrease in the gamma-S parameter in leacril fabric at concentrations of N-CP-Cl in solution as the fabric is treated is due to the decreasing content of sulfonate and sulfate groups electron donors, in the leacril due to acid-base neutralization between the cation of the surfactant and the surface groups of the fabric. The obtained value of gamma-S, 35.8 mJ/m2, after the treatment of leacril with 10(-2) M N-CP-Cl could be due to the presence of N+-pyridinium groups, electron donors, on the leacril surface at the highest concentrations of surfactant due to the adsorption of the surfactant onto the leacril surface.