The secretory proteins of the mucosa of the cervix, uterus, and fallopian tubes were investigated by measuring the proteins that were released by isolated mucosal areas. Initial screening disclosed that the immunoglobulins IgG and IgA were released in measurable quantities, but that IgM and the secretory (T) piece of IgA were either absent or present only in trace amounts. Relatively low levels of diffusable total complement activity and the C3 component of complement were present, whereas the C1q, C1r, and C4 components were either absent or present only in trace quantities. No neutral proteinase activity was present, but lysozyme, plasminogen activator, alpha 1-antitrypsin, and alpha 1x-antichymotrypsin could be found in reasonable amounts. The site of secretion, concentration, and cyclic variation of the proteins that diffused from the mucosal sites in measurable quantities were studied. The types and amounts of protein secreted by a particular site in the cervix, uterus, or fallopian tube varied from those of protein from other sites, even within the same organ. During the menstrual cycle, variations occurred in the amount of protein secreted by each mucosal site. However, whether an increase or a decrease in the release of a particular protein took place varied with each protein, even at the same site. The mucosal sites also differed from each other in their response to the phase of the menstrual cycle, that is, whether more or less protein was released, even sites within the same organ. The conclusion is that each organ and even different sites within an organ can respond independently from each other to changes in hormone levels, producing different types and amounts of secretory proteins. The amount of diffusable protein produced by an individual site during the menstrual cycle depends on the type of protein as well as the mucosal site.