Nanocrystalline FeTi has been prepared in two ways: by ball milling the intermetallic compound and mechanically alloying a mixture of the elemental powders. The materials obtained in each case are identical. The reaction proceeds via the formation of interfacial β–Ti(Fe) which then grows to include all of the material present. Oxygen levels above 3 at. % suppress this reaction and lead to the formation of amorphous Fe–Ti.