The paper presents an impedance analysis of SrTiO3 thin films with La, Fe, and Mn, respectively, as heterovalent substituents. The films were prepared by chemical solution deposition. Dopant concentrations were varied in the range from 0.1 at% to 5 at% for the electrical studies. Aluminum as a low-workfunction metal was employed as the cathode electrode. The current response upon a d.c. voltage step stimulation was analyzed with respect to the relaxation, leakage, and degradation behaviour. The results show that La, as a donor-type substituent, tends to increase the leakage while it reduces the resistance degradation. Low concentrations of Fe and Mn, respectively, decrease the leakage current considerably while at higher dopant concentrations the leakage current increases again. The lifetimes are improved by Mn doping and, to a lesser extent, by Fe doping, The dielectric losses and the corresponding relaxation currents are only slightly affected by the dopants. The results are discussed in a comparison with literature data on comparable bulk ceramics and in the light of the defect chemistry of alkaline earth titanates.