Steady state fluxes obtained during cross-flow filtration of pseudoplastic guar gum solutions are correlated to four hydrodynamic parameters: the cross-flow velocity, the wall shear stress, the Reynolds number generalised for power law-fluids and wall sheer rate. A mean concentration of the boundary layer at the membrane wall was taken into account to calculate the generalised Reynolds number and wall shear rate. This concentration was identified by fitting the experimental friction factors to the Poiseuille law according to the method described in [H. Carrere, F. Rene, Exp. Fluids 25 (1998) 243-253]. Some parameters of the correlations were expressed as a function of the mean boundary layer structure index. Description of the hydrodynamic effects on the steady flux was not the same according to the parameter used. The wall shear stress effect was the greatest whereas the shear rate and the generalised Reynolds number effects were the lowest for the more pseudoplastic fluids. The cross-flow velocity effect presented a maximum within the studied concentration range.