AIMS: The study aimed to evaluate the effects of probiotic Lactobacillus reuteri DSM 17938 strain supplementation in patients suffering from systemic nickel allergy syndrome, in terms of modulation of faecal LAB population linked to a reduction of GI and cutaneous symptoms and to an increase of patient's quality of life. METHODS AND RESULTS: A preliminary double-blind randomized placebo-controlled study was planned and a culture-independent method based on denaturing gradient gel electrophoresis (DGGE) analysis coupled to the 16S rRNA gene sequencing was applied to investigate on the dynamics of faecal LAB communities before and during a low-Ni diet, supplemented with the probiotic strain. Moreover, the severity and the frequency of GI and cutaneous reactions as well as patient's clinical condition perception (VAS scores) were estimated by statistical analysis. PCR-DGGE fingerprinting obtained using LAB-specific primers revealed significant shift in faecal community with an increase in biodiversity in patients supplemented with probiotic Lact. reuteri strain. In addition, GI reactions such as symptoms related to meals and type of stools significantly improved only in patients treated with Lact. reuteri, while severity and frequency of cutaneous symptoms (urticaria, itch and eczema) and recurrent abdominal pain (RAP) as well as VAS scores statistically decreased in both groups. CONCLUSIONS: Our preliminary findings suggest that probiotic Lact. reuteri could be a useful supplementation during a low-Ni diet of patients with SNAS, to increase LAB population diversity, which could contribute to restore the intestinal homoeostasis conditions. SIGNIFICANCE AND IMPACT OF THE STUDY: To date, no information is available on probiotics application and on their effects, in terms of intestinal microbiota modulation, on patients suffering from SNAS. Therefore, the identification of dominant LAB community and the study of its shift during the probiotic supplementation could enhance the knowledge of the SNAS syndrome.