Serum was collected from individuals with little, average, or extensive exposure to mosquito bites for determination of the presence of circulating antibodies to mosquito salivary gland proteins. Intensity of exposure was determined by mosquito-bite and exposure history. Sections cut through the thorax of four different species of mosquitoes, locally prevalent in South Florida, were exposed to serum and developed for antibody binding with the use of the avidin-biotin-peroxidase immunohistochemical technique. In subjects with histories of little or average exposure to mosquitoes, binding was observed that appeared to be species-specific; in subjects with extensive exposures, little antibody binding to salivary gland was noted. We hypothesize that suppression of the humoral immune response is an adaptive mechanism in response to significant exposures of mosquito salivary gland antigens.