Nanocrystalline MmNi(5)-type alloys have been prepared by mechanical alloying (MA) followed by annealing. The structural and electrochemical properties of these materials have been investigated at room temperature. The amorphous phase forms directly from the starting mixture of the elements, without other phase formation. Heating the MA powders at 1070 K for 1 h resulted in the formation of the hexagonal CaCu5-type structure. For nanocrystalline MmNi(4.2)Al(0.8) material discharge capacities of 207 mAh g(-1) were obtained. (C) 1999 Elsevier Science S.A. All rights reserved.