Immunologic analyses of sera from 47 selected individuals living in a mixed filariasis transmission zone in Gabon were carried out. Onchocerca volvulus, Loa loa, Mansonella streptocerca, and M. perstans are transmitted in this region. Based on parasitologic findings and age, the 47 individuals were stratified into four groups: microfilaria negative (Mf-) children (3–15 years old), Mf- adults (> 15 years old), microfilaria positive (Mf+) children and Mf+ adults. For descriptive purposes, the term microfilaria positive refers to individuals with skin and blood microfilariae. Antifilarial antibody titers were determined using an enzyme-linked immunosorbent assay with Dipetalonema viteae antigens. In general, children had higher titers of IgG antibodies than adults. For the IgG1, IgG2, and IgG3 subclass responses, both age and microfilarial status appeared to be important variables since Mf- children consistently had the highest titers whereas Mf- adults had the lowest titers. For the IgG4 antifilarial response, only the microfilarial status was an important variable. All Mf+ individuals had significantly higher levels of IgG4 antibody than Mf- individuals. Pooled sera of Mf- and Mf+ individuals reacted with similar O. volvulus antigens on Western blots. Control sera of individuals who did not reside in the study area, but who had single infections with L. loa or M. perstans, did not react with any O. volvulus antigens.