A systematic study of the electrical and infrared properties of the high critical temperature, T-c, compound superconductor GdBa2(Cu1-xPbx)(3)O-delta has been performed. Resistivity and a.c. susceptibility measurements show a significant drop in T-c when copper is replaced by lead in the range 0.005 less than or equal to x less than or equal to 0.025 Infrared measurements show that the conductivity of the compound increases with the increase in lead concentration. For undoped samples, all the Restrahlen vibrations, common to these materials, are present in the infrared reflectance spectra. As the concentration of lead is increased, a shift of the phonon modes, as well as broadening of the 150 cm(-1) phonon mode, is observed. Also the Restrahlen vibration around 410 cm(-1) present in the normal material starts to disappear. This 150 mode is attributed to a change in the oxygen concentration, and is shown to be correlated with the critical temperature.