Samples fabricated by pressure-infiltration of nickel powders with molten aluminium were heat treated at 1 200-degrees-C under vacuum or argon isostatic pressure. Reaction and diffusion in the as-infiltrated samples, which contained nickel, aluminium and varying amounts of Ni2Al3 and Al3Ni, resulted in the formation of NiAl as a principal phase with nickel and Ni3Al as minor phases. All samples exhibited macroporosity due to the formation of an interconnected transient liquid phase during heat treatment. Vacuum-annealed samples also showed extensive Kirkendall porosity in the nickel phase, which was, however, pore-free in hot isostatically pressed samples due to compaction during reaction. Concentration profiles of aluminium in these nickel regions were measured and are in good agreement with predicted values.