This paper investigates the crystal structure, thermal expansion, and electrical conductivity of two series of perovskites (LaMn0.25-x Co0.75-x Cu-2x O3-delta and LaMn0.75-x Co0.25-x Cu-2x O3-delta with x = 0, 0.025, 0.05, 0.1, 0.15, 0.2, and 0.25) in the quasi-ternary system LaMnO3-LaCoO3-"LaCuO3". The Mn/Co ratio was found to have a stronger influence on these properties than the Cu content. In comparison to the Co-rich series (LaMn0.25-x Co0.75-x Cu-2x O3-delta), the Mn-rich series (LaMn0.75-x Co0.25-x Cu-2x O3-delta) showed a much higher Cu solubility. All compositions in this series were single-phase materials after calcination at 1100 A degrees C. The Co-rich series showed higher thermal expansion coefficients (alpha(max) = 19.6 x 10(-6) K-1) and electrical conductivity (sigma(max) = 730 S/cm at 800 A degrees C) than the Mn-rich series (alpha(max) = 10.6 x 10(-6) K-1, sigma(max) = 94 S/cm at 800 A degrees C). Irregularities in the thermal expansion curves indicated phase transitions at 150-350 A degrees C for the Mn-rich series, while partial melting occurred at 980-1000 A degrees C for the Co-rich series with x > 0.15.