PRIMITIVE meteorites (carbonaceous chondrites and unequilibrated ordinary chondrites) are isotopically heterogeneous, indicating that the material from which the Solar System formed was not completely homogenized(1-4). On the other hand, isotopically heterogeneous material is not expected to survive in thermally ’processed’ planetary or asteroidal objects. The achondrite meteorite Acapulco is a remnant of one such object; its petrographic and trace-element characteristics suggest that the parent body experienced pervasive heating and partial melting(5). Here we report the discovery of graphite grains in the Acapulco meteorite that have a wide range of carbon and nitrogen isotopic compositions (delta(13)C ranging from -34 to -8 parts per thousand and delta(15)N from -154 to -67 parts per thousand). The graphite is associated with metal, and in some cases, graphite grains associated with the same metal grain have very different isotopic compositions. These findings suggest that the graphite grains retain the isotopic signatures of a diverse range of precursor materials, despite the high temperatures reached in the parent asteroid.