The effect of Ag on the microstructure of NiAl was investigated by Optical Microscopy, X-ray diffraction, Electron Probe Microanalysis and Transmission Electron Microscopy. The NiAl-Ag alloys consisted of two phases: beta-NiAl and Ag-rich solid solution. The amount of the Ag-rich phase increased with increasing Ag content. Ag has very low solubility in NiAl and they form pseudo-binary monotectic systems. (C) 2002 Elsevier Science B.V. All rights reserved.