When the immunological mechanism of the demodectic mange is well-known in dogs, few things are known about the role of Demodex mites in the pathogenesis of rosacea: the purpose of this study is the research of immunological reactions against Demodex antigens in 31 patients (24 papulopustular rosaceas and 7 granulomatous demodectic rosaceas histologically ascertained). Cultures or survival in vitro of human Demodex mites could not be obtained; therefore demodectic cysts of diseased goats (Demodex caprae) were gathered and soluble antigens were extracted by lyophilization. By different immunoserological methods, Demodex specific antibodies could be demonstrated in sera of rosacea (22%), of diseased goats and of rabbits sensitized with small amounts of demodectic antigen. Frequently cross-reactions were observed.