The stoichiometry, polymorphism and electrical behaviour of solid solutions Li0.5-3xPr0.5+xTiO3 with perovskite-type structure have been studied. Data are shown in the form of a phase diagram, XRD patterns for the three polymorphs, A, C, and beta, temperature- and composition-dependence of their lattice parameters and Arrhenius conductivity plots. Microstructure and composition were studied by electron probe microanalysis. Maximum conductivity is 4 x 10(-6) S cm(-1) at 25 degrees C for x = 0.08. An insulating surface layer, seen in samples coated with Au electrodes, disappears in contact with molten LiClO4.