In an extension of earlier work, the response of niobium-niobium point-contact Josephson junctions to radiation from hydrogen cyanide and deuterium cyanide lasers has been studied. Constant voltage steps corresponding to the 805, 891 and 964 GHz lines from a HCN laser have been observed as well as steps corresponding to the frequency mixtures of all these lines. In addition, subharmonic and harmonics of `mixed-frequency' steps have also been observed. The first observation of Josephson step structure corresponding to the 1540 and 1578 GHz emissions of a DCN laser is reported.