Knowledge of the differences in radiated susceptibility (RS) testing in anechoic (AC) and reverberation chambers (RC) is essential for analysis of the susceptibility of electronic systems to microwave radiation. We have studied microwave field-to-wire coupling for some basic wire geometries above a ground plane in ACs and RC. Results for receiving parameters such as the antenna receiving cross section and the effective antenna length of the wire, he, are presented. The ratio between the maximum and average values of the antenna receiving cross section may exceed 15 dB in the AC, the average being equal to the antenna receiving cross section measured in the RC. Large variations in the antenna receiving cross section show that the outcome of an RS test in an AC may depend strongly on the direction and polarization of the incident field. For a realistic RS test in ACs only a few angles of incidence can typically be afforded, implying a substantial risk for undertesting. Furthermore, the antenna receiving cross section measured in the RC follows a Chi-square-distribution with two degrees of freedom. The measurements in the AC do not follow the same distribution.