New ternary and quaternary transition-metal chalcogenides have resulted from substitutional chemistry of known phases. Ta2Ni3S8 and Ta2Pt3Se8 have been synthesized and characterized by single-crystal X-ray techniques. These compounds adopt the Nb2Pd3Se8 structural type. Hence in Ta2Ni3S8 Ni occupies both square-planar and square-pyramidal sites as similarly does Pt in Ta2Pt3Se8. The electrical conductivity of Ta2Ni3S8 establishes its semiconducting behavior. Ta has been substituted for Nb in the Nb2Pd0.71Se5 type to yield Ta2Pd0.89S5 which has been characterized by single crystal X-ray techniques. The square-planar Pd sites in the van der Waals' gap of this layer structure are 78.6(4)% occupied. This compound shows metallic behavior. The compound Co2Nb4PdSe12 has been synthesized and characterized by single-crystal X-ray techniques. It is of the Co2Ta4PdSe12 structural type and thus contains Nb in both trigonal prismatic and octahedral sites.