A technique is presented to estimate ice cloud particle characteristic sizes and concentrations as well as the integrated ice water path from simultaneous ground-based radar and infrared radiometer measurement. The approach is based on the theoretical consideration of infrared thermal radiative transfer within a cloud and can be applied to clouds that are semitrasparent in the infrared ''window'' and horizontally extensive. The suggested technique is applied to radar and infrared radiometer data collected during the Cloud Lidar and Radar Exploratory Test (CLARET-I) experiment. Retrieved values of ice cloud microphysical parameters are in general agreement with results obtained by other methods. ¿ American Geophysical Union 1992