The nasal polyp (NP) seems to represent the end-stage of longstanding inflammation in patients with chronic rhinosinusitis.The aim of our study has been to evaluate the presence of two regulatory cell populations in the microenvironmentof NP: CD4+CD25high Foxp3+ (Treg) cells and B7-H4-expressing macrophages. Treg cells are actively able to inhibitT lymphocytes, while the population of B7-H4-expressing macrophages has recently been described as characterized bya regulatory function similar to that of Treg cells. For our study, we evaluated 14 NP tissue samples. The samples were dividedinto two main groups, eosinophilic (NP) and lymphocytic (NP), according to the predominant type of immune cell infiltration.The presence of Treg cells and B7-H4 positive macrophages in the samples was analyzed by FACS. Treg cells andB7-H4-expressing macrophages were identified in all the examined nasal polyps. The percentages of both Treg cells and ofB7H4 positive cells found in the eosinophilic nasal polyps were higher than those found in the lymphocytic nasal polyps.Treg cells and B7H4+ macrophage subpopulations were present in the NP microenvironment and the alterations in their percentageswere related to a distinct pattern of immune cell infiltration.