Some evidence for the specification of white marbles by Greek and Roman sculptors, contractors, and clients is briefly reviewed. The value to archaeologists and art historians of identifying white marbles is considered. Some methods of identification are discussed: in particular, the advantages and limitations of carbon and oxygen stable isotope analysis. A report follows on a preliminary program of isotopic analysis of Roman sarcophagi in the collections of the British Museum, illustrating the application of this technique to solving problems of associating particular sarcophagi in pairs or groups. These may reflect the products of a particular workshop, or the linking of workshops with known quarries. Imitations of well-known types of sarcophagus, made of marble not normally associated with the type, may also be identified with the aid of isotopic analysis. The technique may help identify workshops located in metropolitan centers far from the quarries, where iconography may not be used to link the finished products of an urban workshop with sarcophagi roughed out at the quarry. Finally, isotopic analysis may help to associate fragments which, if they belong to the same object, would have been cut from the same block of marble. -- AATA