Exploration of the sodium-gallium-nickel system has revealed a new compound containing the isolated gallium clusters Ga10Ni10-. Single-crystal X-ray diffraction studies of Na10Ga10Ni (Pnma, Z = 12, a = 13.908(3) Angstrom, b = 78.146(6) Angstrom, c = 16.286(4) Angstrom) show it to be isostructural with K10In10Ni. The compound contains two similar "naked" gallium clusters as distorted, tetracapped trigonal prismatic units that are centered by nickel. The sodium atoms serve to isolate the clusters from each other as well as to provide the cluster with a closed shell configuration of electrons. This is the first isolated gallium cluster in an alkali-metal system that is centered. Molecular orbital calculations on the cluster are also reported. The crystal structure of K2Ga3 (I4/mmm, Z = 4, a = 6.1382(3) Angstrom, c = 14.815(1) Angstrom) has also been established to be isostructural with A(2)In(3) (A = Rb, Cs). This contains Ga-6(4-) octahedra interconnected through the waist atoms into layers (2)(infinity)[Ga-6(])4-, with octahedra in adjacent layers sitting in the depressions of the first. The potassium atoms have characteristic roles except for an unusually short K-K contact (3.242(4) Angstrom) across the layer. Magnetic measurements indicate that both phases are diamagnetic and consistent with the Zintl formalism.