CCR6 expression in dendritic, T, and B cells suggests that this beta-chemokine receptor may regulate the migration and recruitment of antigen-presenting and immunocompetent cells during inflammatory and immunological responses. Here we demonstrate that CCR6-/- mice have underdeveloped Peyer's patches, in which the myeloid CD11b+ CD11c+ dendritic-cell subset is not present in the subepithelial dome. CCR6-/- mice also have increased numbers in T-cell subpopulations within the intestinal mucosa. In 2,4-dinitrofluorobenzene-induced contact hypersensitivity (CHS) studies, CCR6-/- mice developed more severe and more persistent inflammation than wild-type (WT) animals. Conversely, in a delayed-type hypersensitivity (DTH) model induced with allogeneic splenocytes, CCR6-/- mice developed no inflammatory response. The altered responses seen in the CHS and DTH assays suggest the existence of a defect in the activation and/or migration of the CD4(+) T-cell subsets that downregulate or elicit the inflammation response, respectively. These findings underscore the role of CCR6 in cutaneous and intestinal immunity and the utility of CCR6-/- mice as a model to study pathologies in these tissues. This article was published online in advance of the print edition. The date of publication is available from the JCI website, http://www.jci.org.