RETC is a program for analyzing the hydraulic conductivity properties of unsaturated soils. The parametric models of Brooks-Corey and van Genuchten are used to represent the soil water retention curve. The theoretical pore-size distribution models of Mualem and Burdine predict the unsaturated hydraulic conductivity function. The simulation can be generated from observed soil water retention data, assuming that one observed conductivity value (not necessarily at saturation) is available. The program also permits users to fit analytical functions simultaneously to observed water retention and hydraulic conductivity data.