Electrochemical solid electrolyte sensors are suited for the reliable measurement of NO in hot exhaust gases of automotive and industrial combustion processes. Important sensor parameters like sensitivity, selectivity and long-term stability are correlated mainly with the performance of the material of the mixed potential electrodes. The aim of this work is the characterization of newly developed perovskite materials from the group La_0.6Ca_0.4Mn_xMe_{1 - x}O_{3 - δ} with Me = Ni, Co and x = 0-0.6 with respect to their electrochemical behavior in NO and C₃H₆ containing gases and its correlation with conductivity and defect chemistry. Maximum sensitivity was found for the materials with Me = Ni and x = 0.2-0.3. EIS measurements show that the NO diminishes the electrode resistance also for materials with no potentiometric sensitivity to NO. Correlating the results of conductivity and oxygen stoichiometry measurements, it seems that n-type conductors are more promising materials for NO detection with mixed potential sensors.