Far infrared reflectivity spectra of single crystal PbTe doped with Bi were measured and numerically analyzed using a fitting procedure based on a modified plasmon-phonon interaction model with two additional oscillators at about 140 and 219 cm(-1) which represents local Bi impurity modes. The position of observed plasma minimum and the values of the calculated parameters were compared with the literature data for pure single crystal PbTe which shows that bismuth improved the basic properties of the host crystal a lot.