The present study reveals some discordancies of diagnosis considering Vibrionaceae strains when tested by comparison with API 20E (BioMerieux) system and classical biochemical reactions, aspects already mentioned in the literature by other authors. If any misidentification has not an important impact (e.g. identification of Aeromonas schubertii as A. sobria), others as misidentification of Aeromonas as Vibrio strains or the failure to recognize Vibrio strains raise major epidemiological problems. The present study was performed on 25 aquatic strains, comparatively identified by means of API 20E system and classical biochemical tests (using media prepared in Vibrio Laboratory of Cantacuzino Institute). All 25 strains were identified as Vibrio fluvialis by API 20E system, while using the classical tests one strain proved to belong to Pseudomonadaceae (O/F test of oxidative type), one was identified as Aeromonas schubertii, 2 Aeromonas hydrophila and 4 Aeromonas caviae. Discordancies between API 20 E system and classical tests were registered for: gelatinase (20%), LDC 12% and ADH, ODH, O/F test, saccharose, manite, inosite (4% each). The misidentification of Aeromonas as Vibrio strains by API 20E hinders the recognition of Aeromonas infections implicated more and more frequently in human pathology in immunodeficient as well as in immunocompetent hosts. Our results demonstrate that the use of API 20E system has some limits in the diagnostic of some bacterial genera (Vibrio, Aeromonas), and the introduction of these systems in the current laboratory practice requires previous information and studies regarding their efficiency and availability for the diagnostic of particular bacterial genera and species.