Mannitol hexaacetate (MHA) has been detected by GC-MS in some brown illicit drug seizures in which diacetylmorphine (DAM) was completely lacking. The presence of MHA as a genuine ingredient of the drug seizures rather than a storage- or an analytical artifact, formed by transacetylation of mannitol with the DAM in the heroin, has been verified. It is argued that MHA was formed as a result of the addition of mannitol, as diluent, before the acetylating step in the process of the heroin preparation. This early dilution in the production and distribution chain of the illicit drug is deemed as peculiar, nonetheless it may be highly indicative of a specific production process of heroin in a trafficking organization. © 2004 Elsevier Ireland Ltd. All rights reserved.