Abstract The observed range in nickel content of iron meteorites may be explained by their having differentiated during the crystallization of an originally homogeneous iron melt containing 11 % nickel which formed the core of a typical parent meteorite body. Quantitative estimates of the relative abundances of the various types of iron meteorites which can differentiate from nickel-iron melts of varying compositions are calculated. Again assuming an original melt of 11 % nickel, the agreement between the calculated relative abundances and new estimates of the observed relative abundances of iron meteorites is very striking. It is significant that the metal phase of stony-iron meteorites, which may be expected to be a sample of the undifferentiated melt, has a mean nickel content of 11 %. The well-known metallurgical phenomenon of “coring” (under conditions approximating complete mixing in the liquid), which causes segregation of solute in the solid phase during the crystallization of alloys, is probably the best analogy to the differentiation process suggested.