The contribution of viscous friction, slippage, the Marangoni effect, and three-phase contact line resistance is considered in the explanation of contact angle measurements using a dynamic method. It is shown that the viscous friction of the liquid and the specific resistance of the three-phase contact line are the basic dissipative forces governing the rheology, while the slip on the solid-liquid interface is not important for this kind of experiment. Since the method is applied to protein solutions, it is demonstrated that the Marangoni effect of the proteins on the liquid-air surface plays an important role in the right juxtaposition of the theoretical and experimental results. Proper application of the theory allows calculation of both receding and equilibrium contact angles from the dropping time measurements as well as their dependence on the concentration of the protein solutions.