The polarised infrared reflectivity of the chalcopyrite structure compound, CdGeAs2, has been measured at room temperature in the range 20-400 cm-1. Five of the six E optical modes and two of the three B2 optical modes have been observed. The transverse optical phonons deriving from G of zinc blende for both E and B2 modes (at 272 and 270 cm-1, respectively) agree in energy with that of the isoelectronic binary, GaAs (at 269 cm-1). The reflectivity spectra of CdGeAs2 have the same general character as other chalcopyrites studied. © 1977.