BACKGROUND AND AIM: The neurotransmitter histamine is involved in the regulation of appetite and in the development of age-related obesity in mice. Furthermore, histamine is a mediator of the anorexigenic action of leptin. The aim of the present study was to investigate a possible role of histamine in the development of high-fat diet (HFD)-induced obesity. METHODS: Histamine-deficient histidine decarboxylase knock-out (HDC-KO) mice and C57BL/6J wild-type (WT) mice were given either a standard diet (STD) or HFD for 8 weeks. Body weight, 24-hour caloric intake, epididymal adipose tissue size, plasma leptin concentration and quantitative expression of leptin receptor (Ob-R) mRNA were measured. RESULTS: Both HDC-KO and WT mice fed an HFD for 8 weeks increased their body weight significantly more than STD-fed mice. A significant difference in body weight gain between HDC-KO mice fed an HFD or an STD was seen after 2 weeks, whereas a significant difference in body weight gain was first observed after 5 weeks in WT mice. After 8 weeks 24-hour caloric intake was significantly lower in HFD- than in STD-fed WT mice. In HDC-KO mice no difference in caloric intake was observed between HFD- and STD-fed mice. After 8 weeks epididymal adipose tissue size and plasma leptin concentration had increased significantly in HFD-fed WT and HDC-KO mice compared to their STD-fed controls. Epididymal adipose tissue size was higher in HDC-KO than WT mice, both in STD- and HFD-fed mice. A significant decrease in Ob-R mRNA in HFD-fed HDC-KO mice compared to STD-fed HDC-KO mice was observed, while no such difference was observed in WT mice. CONCLUSION: Based on our results, we conclude that histamine plays a role in the development of HFD-induced obesity.