Recently, the diffusion on the black market of new psychoactive substances not controlled and often sold as ‘legal highs’, is exponentially increasing in Europe. Generally, the first analysis for these drugs involves an immunoassay screening in urine or plasma. Actually, there is growing interest in the use of oral fluid (OF) as alternative specimen over conventional biological fluids for drug testing, because of the significant advantages, as a non-invasive collection under direct observation without undue embarrassment or invasion of privacy, and a good correlation with plasma analytical data. Few assays have been developed for detection of new psychoactive compounds in biological samples, so it is important to investigate how they may or may not react in pre-existing commercial immunoassays. In this paper, two different multi-drugs oral fluid screen devices (OFDs) (Screen Multi-Drug OFD and GIMA One Step Multi-Line Screen Test OFD) were evaluated to determine the cross-reactivity of thirty-nine new amphetamine designer drugs, including twelve substances officially recognized as illicit by italian legislation. Crossreactivity towards most drugs analyzed was <1 in assays targeting amphetamine (AMP) or methamphetamine (MET). Only two (p-methoxyamphetamine and p-methoxymethamphetamine) of all tested amphetamines gave a positive result.