I investigate which mechanisms could have acted during Neptune's past radial migration to excite plutino orbital inclinations to their present values. These processes include Kozai resonance and the ν18 secular resonance, both before and after the plutino's capture into the 2 : 3 mean motion resonance with Neptune. In the case that ν18 acted before the 2 : 3 resonance encounter, the plutino would have been originally formed near 34 AU. If the plutino was captured near the beginning of the migration process at around 30.5 AU, then the secular resonance must have acted inside the 2 : 3 resonance with high-amplitude libration. In this case, the libration amplitude must be damped either during the migration by some dynamical process or after migration through dynamical scattering by other Kuiper belt objects, thus making the final orbit stable. All plutinos with well-determined orbits and inclination above 10° seem to have undergone secular resonance.