The effect of the substitution of Mn with In in the magnetoresistive La 2/3 Ca 1/3 MnO 3 compound has been studied by means of X-ray diffraction, a.c. magnetic susceptibility, d.c. magnetization, and d.c. resistance techniques. This substitution is possible for x4 40.07 under normal synthetic procedures. The Curie temperature decreases with increasing x in La 2/3 Ca 1/3 Mn 1؊x In x O 3 . Samples with x5 50.05 do not show long-range ferromagnetic order but rather a cluster-glass behavior. Magnetic inhomogeneities, arising both from random substitution of Mn with In and from formation of oxygen vacancies, can lead to such behavior. Samples with x5 50.05 do not show metal-insulator transition. 1998 Academic Press EXPERIMENTAL SECTION La Ca Mn \V In V O (x"0, 0.01, 0.03, 0.05) samples were prepared by standard ceramic procedures. Stoichiometric amounts of La O , CaCO , In O , and MnCO , with nominal purities not less than 99.99%, were mixed and heated in air at 950°C for 12 h. After grinding, they were pressed into bars and sintered in air at 1250°C for 48 h and at 1400°C for 12 h with intermediate grindings. Samples with x"0, 0.03, 0.05, 0.07, 0.1, 0.15, and 0.3 were prepared