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Abstract  The hydrogen (H2) lactose breath test (BT) is a test commonly used for the diagnosis of hypolactasia. However, its sensitivity is not always good. In the last few years, the new Quick Lactase Test (QLT) has been developed for endoscopic diagnosis of adult-type hypolactasia. The aim of this study was to compare the efficacy of the new QLT with the traditional H2 lactose BT for the diagnosis of hypolactasia. Fifty dyspeptic patients (19 male, 31 female, mean age 38 ± 6) were enrolled in the study. All the patients were subjected to the H2 lactose BT and to upper gastrointestinal endoscopy. Two postbulbar duodenal biopsies were used for the QLT (Biohit, Helsinki, Finland). The duodenum biopsies were incubated with lactose on a test plate: in patients with normolactasia a colour reaction develops as a result of hydrolysed lactose (positive result), whereas no reaction develops in patients with mild or severe hypolactasia (negative results). Twenty-two out of 50 patients (44%) had a positive H2 lactose BT. Among them, 21 showed a mild or severe hypolactasia with the QLT. When we considered patients with a negative H2 lactose BT (28 out of 50), 24 patients showed normal lactase activity in duodenal biopsies with the QLT, whereas in 4 patients there was discordance between the two tests. These patients were re-evaluated with a methane (CH4) and an H2 lactose BT and 3 of them were H2 non-producers with a high level of CH4 production. Only 1 patient with a negative result in the QLT remains negative to lactose BT. Our study showed a good correlation between the H2 lactose BT and the new QLT in the diagnosis of adult-type hypolactasia for the majority of patients. However, the QLT seems to be more sensitive than the H2 lactose BT, helping to identify a subgroup of patients with adult-type hypolactasia with a negative result in the H2 lactose BT. Based on these results we suggest performing the less expensive and more rapid QLT during the upper gastrointestinal endoscopy to evaluate the presence of lactase activity in duodenal biopsies. [ABSTRACT FROM AUTHOR]