In this paper, we examine the possible influence of extrinsic factors on the electrical and magnetotransportof La0.67Ca0.33Mn1−xRuxO3 (x≤0.10). Ru substitution results in double metal–insulator transitions (MITs) atTMI1 and TMI2, both exhibiting magnetoresistance (MR). No additional magneticsignal corresponding to a second low-temperature maximum (LTM) atTMI2 could be observed, either in ac susceptibility(χ′) or in specificheat (Cp). Typicalgrain sizes of ∼18 000–20 000 nm, as estimated from the scanning electron microscope (SEM) micrographs, are notso small as to warrant an LTM. The absence of additional peaks in the highstatistics powder x-ray diffraction (XRD), a linear systematic increase of theunit cell parameters, close matching of the transition temperatures in resistivity,χ′ andCp and their linearsystematic decrease with x, and an homogeneous distribution of Mn, Ru and O at arbitrarily selected regions withinand across the grains exclude chemical inhomogeneity in the samples. The insensitivity ofgrain boundary MR at 5 K to Ru composition indicates that the grain boundary is notaltered to result in an LTM. Oxygen stoichiometry of all the compounds is close to thenominal value of 3. These results not only exclude the extrinsic factors, but alsoestablish that double MITs, both exhibiting MR, are intrinsic to Ru substitutedLa0.67Ca0.33MnO3.