Abstract. The applicability of the method of summed amplitudes of coinciding pulses to determine radiative strength functions of heavy nuclei by measuring two-step cascade ?J-ray spectra is discussed. Experiments based on thermal neutron capture in 136Ba and 18~ were carried out to test this method. The values obtained for the radiative strength functions of a wide range of primary transitions were compared with the predictions of two modifications of the giant dipole resonance model. Some insight into the characteristics of the y-decay of compound-states is provided by analyzing the information obtained on the two-step ?,-decay of a number of nuclei in the mass region 137 _< A_ 187.