This paper reports on a laboratory experiment that investigates the use of active microwave observations to estimate volumetric soil moisture content. The experiment, held in 1995, was set up at the European Microwave Signature Laboratory, Joint Research Center of the European Communities, Ispra (Italy). Full polarimetric radar observations of a 2 m diameter cylindric container filled with a sandy loam soil were performed. During successive wetting and drying cycles, different soil moisture profiles were generated and observed in situ by means of time domain reflectometry probes. The radar data are analyzed based on the Integral Equation Model that simulates radar backscattering given known surface characteristics, such as moisture content and roughness. This allows the evaluation of the predictive power of the simulation model. We find general good agreement between measurements and simulations, but problems occur at high incidence angles. The model is then used to invert soil moisture information from radar measurements. It is shown that, in spite of the complexity of the model involved, it is possible to retrieve under certain circumstances reliable soil moisture estimates with similar accuracies as the in situ measurements. ¿ 1999 American Geophysical Union