Temperature and humidity retrievals from an international network of ground-based microwave radiometers (MWR) have been collected to exploit the potential for data assimilation into Numerical Weather Prediction (NWP) modeling. This activity is carried on in the framework of the Hydrological cycle in the Mediterranean Experiment (HyMeX). The domain under analysis is the HyMeX West Mediterranean (WMed) target area, using data assimilation tools developed for the Météo-France Arome-WMed NWP system. In this paper we introduce the data set, discuss results concerning the observation-background statistics, and present preliminary results on the impact of MWR data assimilation into NWP. © 2014 IEEE.