The dilational surface elasticity 6 and the dilational surface viscosity eta of the two nonionic surfactants n-dodecyl-beta-D-maltoside (beta-C(12)G(2)) and tetraethyleneglycol-monodecyl ether (C10E4) were studied using the oscillating drop method. The experiments were carried out at different concentrations and frequencies with an accessible frequency range of 0.005-0.2 Hz. The results are discussed in the light of previous disjoining pressure measurements that demonstrated that the stability of thin liquid films cannot be explained solely by the agnitude of the surface forces. Indeed, a comparison of the results obtained for beta-C(12)G(2) with those obtained for C10E4 reveals a correlation between the stability of the films and the surface dilational elasticity of the respective monolayers.