The method of Joanny and de Gennes of equating the rate of viscous dissipation to the rate of surface work is used for two kinds of non-Newtonian fluids, one in which the rheological coefficients are not constants but the constitutive equation allows no normal stresses (Ellis' model) and the other in which the coefficients are constants but normal stresses arise. the result for the wetting rate and the manner in which it depends on dynamic contact angle which essentially arise from the balance between the viscous and the surface forces are discussed.