The theory of in-situ experiments destined to obtain the information about the relative permeability for gas-condensate mixtures is elaborated. Theoretical basis is the analytical solution of the nonlinear problem of flow towards a well obtained by the asymptotic methods of singular perturbation theory. Analysis of the solution has shown the saturation field to be sensible to some particular modes of flow rates variation in time, which comprises as increasing, as decreasing of the flow rate. Analyzing the hysteresis loop of the wellbore saturation as the function of flow rate, we define the relative permeability for liquid. The relative permeability for gas results from the measurement of the borehole pressure.