Saliva is a readily available specimen that can be collected by non-invasive procedures and contains many drugs of interest in screening and diagnosis. It is obtained by a painless and non invasive method of sampling; it contains the free fraction of drugs and therefore it is a good indicator of intoxication state. Inspite of its usefulness, only a few studies on long-term storage have been conducted for some drugs of abuse, while methadone stability have not been investigated yet. This lack in standardization and the scarcity of analytical protocols actually restrict saliva applications. Authors studied methadone stability on saliva during 12 months. Fifty-nine saliva samples were collected from heroin addicts in methadone treatment with the Cozart Rapiscan Collection procedure. The samples, spiked with tri-deuterated internal standards analogs of methadone and 2-ethyl-1,5-dimethyl-3,3-diphenylpyrrolinium perchlorate (EDDP), were submitted to Solid Phase MicroExtraction-Gas Chromatography/Mass Spectrometry (SPME-GC/MS) technique. Quantitative determinations of methadone and EDDP were performed immediately and after various intervals (one month, two months, twelve months). The results obtained from this experiment show that methadone is sufficiently stable at 4° C until 2 months, while a decrease have been observed for EDDP. These preliminary data prove the need to perform the analysis in a brief time, to avoid loss of EDDP. For the correct use of this biological matrix, more research and guidelines are recommended for drug testing on saliva.