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Fifty new ternary compounds Ln2T3Zn14 were isolated from alloys with a high zinc content by dissolving the zinc-rich matrix in hydrochloric acid. They crystallize with an ordered version of a binary structure type first reported for Th2Zn17. The structure of the ternaries was determined from four-circle X-ray diffractometer data of the four compounds Gd2Co3Zn14, Ce2Rh3Zn14, Pr2Ni3Zn14, and Sm2Pd3Zn14. It is rhombohedral, space group R&thremacr;m, with Z = 3 formula units in the corresponding hexagonal cell and the lattice constants a = 887.2(2) pm and c = 1300.2(3) pm for Gd2Co3Zn14. The transition metal atoms T are located essentially at one atomic site corresponding to the ideal occupancy in the compounds Gd2Co3Zn14 and Pr2Ni3Zn14. For the other two compounds significant deviations from the ideal composition could be observed for three of the four zinc sites of Th2Zn17, with mixed T/Zn occupancy, resulting in the compositions Ce2Rh1.90(2)Zn15.10(2) and Sm2Pd1.92(1)Zn15.08(1). The structure may be viewed as consisting of layers extending perpendicular to the hexagonal axis. One layer contains all of the rare earth atoms, the other all of the transition metal atoms, and both with additional zinc atoms, with unit mesh contents of Ln2Zn6 and T3Zn8. These layers alternate, corresponding to the formula Ln2Zn6·T3Zn8 = Ln2T3Zn14. The structure contains two kinds of voids. One of these is filled by carbon and nitrogen atoms in ternary magnetic materials Ln2Fe17C3-x and Ln2Fe17N3-x. The structure refinements show that both of these voids are unoccupied in the ternary zinc compounds Ln2T3Zn14. Similarly, a structure refinement of the known binary compound La2Zn17 did not reveal any significant amounts of impurity atoms (e.g., oxygen) at these voids. The refinement of the occupancy parameters for this compound resulted in the composition La2Zn16.06(6).