Carbohydrate antigens from Candida albicans, essentially mannan, have previously been shown to persist in the serum of some patients with chronic mucocutaneous candidiasis, and to be able to inhibit specifically the candida antigen-induced proliferation of control lymphocytes. Lymphocytes from three out of six patients were shown to be hypersensitive to mannan inhibition. These data were explained by the demonstration of an apparently selective impairment of radiolabelled mannan handling by two patients' monocytes following a normal uptake. This defect was observed both in active and remission phases of the infection suggesting an intrinsic defect of patients' monocytes. In experiments performed with control lymphocytes, it was shown that mannan exerted its suppressive effect by interfering with candida antigen presentation by adherent cells to autologous T lymphocytes. Furthermore, mannan neither was cytotoxic nor induced suppressor T cells. Altogether, these data suggest that the in vivo persistance of mannan, in some patients, is secondary to a primary macrophage dysfunction leading to impairment of specific cellular immune responsiveness.