Current grain refinement methods for Ti-Al alloys rely on the addition of boron in order to inoculate the melt. This results in the presence of precipitates in the as-cast material. Isomorphic inoculants were developed for a β-solidifying Ti-46Al (at%) alloy in order to grain refine the as-cast ingots without forming precipitates which may survive processing. These inoculants are designed such that rather than nucleating new solid as in traditional inoculation, solidification occurs by direct epitaxial growth of the particles. As such they must be of the same phase and have similar lattice spacing as the solidifying melt. This minimizes the energy barrier for solidification and allows the majority of particles added to the melt to participate in solidification rather than just certain size fractions. A Ti-10Al-25Nb was designed as an isomorphic inoculant with is β and has less than a 2% lattice mismatch with the bulk at high temperature. Isomorphic inoculation was successful with this alloy, both reducing the grain size and increasing the equiaxed fraction of the as-cast ingots. Additionally complex inoculant-melt interactions were found to increase the effectiveness of the particles added to the melt beyond a 1:1 particle:new grain ratio.