The crystal structure of new ternary aluminides (\mathrm{Ce}{2-x}) (\left(\mathrm{Ag}{0.42} \mathrm{Al}{0.58}\right){17} \mathrm{Ag}{y}) with (x=0.39, y=0.18\left(\mathrm{Dy}{2-x}\left(\mathrm{Ag}{0.46} \mathrm{Al}{0.54}\right){17} \mathrm{Ag}{y}\right.) ((x=0.25, y=0.23))-type structure), (a=9.3742(2), c=9.1525(3)) (\AA), (R=0.059)), and (\mathrm{Ce}\left(\mathrm{Ag}{0.58} \mathrm{Al}{0.42}\right){11}\left(\mathrm{BaCd}{11}\right.)-type structure, (a=) 11.0466(3), (c=7.1101(5) \AA, R=0.066)) have been determined using (\mathrm{X})-ray powder diffraction data and Rietveld least squares refinement. Isotypic compounds (R E_{1.6}(\mathrm{Ag}, \mathrm{Al}){17}\left(\mathrm{Dy}{2-x}\left(\mathrm{Ag}{0.46}\right.\right.) (\left.\mathrm{Al}{0.54}\right){17} \mathrm{Ag}{\mathrm{y}})-type structure) with (R E=\mathrm{La}, \mathrm{Pr}, \mathrm{Nd}), and (\mathrm{Sm}) and (R E\left(\mathrm{Ag}, \mathrm{Al}{11}\left(\mathrm{BaCd}{11}\right.\right.)-type structure) with (R E=\mathrm{La}) and (\mathrm{Eu}) have been synthesized and their lattice constants have been determined. o 1994 Academic Press. Inc.