A method is proposed for estimating the unsaturated hydraulic conductivity from observed infiltration data. Infiltration measurements are generally easier to obtain than experimental data required for in situ determination of the hydraulic conductivity. The problem was formulated in terms of a nonlinear least-squares parameter optimization method which combines Philip's two-term infiltration equation with an analytical description of the unsaturated soil hydraulic properties according to Mualem and van Genuchten. Reliable estimates for the hydraulic parameters could be obtained with an inverse procedure when independently measured water retention data were included. The results indicate that soil water content measurements at very low values of the soil water pressure head are especially important to ensure parameter uniqueness. The method provides rapid and cost-effective estimates of the hydraulic properties of field soils.