The reaction of [Pt(AuPPh(3))(8)](NO3)(2) with AgNO3 under H-2-atmosphere yields two new hydride-containing Pt-Au-Ag cluster compounds : [Pt(H)(AgNO3)(AuPPh(3))(8)](NO3) (1) and [Pt(H)(AgNO3)(2)(AuPPh(3))(8)](NO3) (2) These reactions show intimate details on cluster growth : the nine-metal-atom particle [Pt(AuPPh(3))(8)](NO3)(2) grows via oxidative addition of H-2, deprotonation and electrophilic addition of Ag+ to a 10- and then to an 11-metal-atom particle, 2. Cluster compounds 1 and 2 were characterized by elemental analyses, ICP analyses, IR and NMR (H-1, P-31 and Pt-195) spectroscopy, and electrical conductivity measurements. The crystal and molecular structures of 1 and 2 have been determined by means of single-crystal X-ray analyses. The compound [Pt(H)(AgNO3)(AuPPh(3))(8)](NO3) crystallizes in space group P2(1), with Z = 2, a = 15.475(7) Angstrom, b = 26.048(2) Angstrom, c = 16.586(2) Angstrom, beta = 97.00(4)degrees, and V = 6636 Angstrom(3). Mo K alpha radiation was used. The residuals are R = 0.070 and wR(2) = 0.170 for 6294 observed reflections and 311 variables. The compound [Pt(H)(AgNO3)2(AuPPh(3))(8)](NO3) crystallizes in space group P (1) over bar in two almost identical modifications. During X-ray measurement the first modification converted into the second modification, with a small loss of crystal solvent molecules. The X-ray analysis of the first modification revealed Z = 2, a = 16.956(3) Angstrom, b = 17.48(1) Angstrom, c = 27.36(2) Angstrom, alpha = 93.68(8)degrees, beta = 97.55(4)degrees, gamma = 76.16(8)degrees, and V = 7802 Angstrom(3); Mo K alpha radiation was used. The residuals are R = 0.055 and wR(2) = 0.151 for 4169 observed reflections and 443 variables. The X-ray analysis of the second modification revealed Z = 2, a = 16.848(4) Angstrom, b = 17.51(4) Angstrom, c = 27.40(3) Angstrom, alpha = 96.3(2)degrees, beta = 95.9(1)degrees, gamma = 72.46(7)degrees, and V = 7639 Angstrom(3). Mo K alpha radiation was used; the residuals are R = 0.090 and wR(2) = 0.230 for 5040 observed reflections and 443 variables. Both clusters, 1 and 2, have a central Pt atom surrounded by eight Au and one (for 1) or two (for 2) Ag atoms; the Au atoms are attached to PPh(3) ligands, and the Ag atoms are coordinated to nitrate. In the PtAgAu8 and the PtAg2Au8 frames, the hydride-ligand is positioned between Pt and Au and is located "trans" to the silver atoms. [Pt(H)(AgCl)(AuPPh(3))(8)](PF6) and [Pt(H)(AgCl)(2)(AuPPh(3))(8)](NO3) can be regarded as the Cl-analogues of 1 and 2 respectively. [Pt(H)(AuPPh(3))(8)](+) (3) has been prepared by deprotonation of the dihydride cluster [Pt(H)(2)(AuPPh(3))(8)](+) using a basic solvent like pyridine.