The presence of antibodies to extracellular polysaccharides (EPS) of moulds in sera of healthy subjects (N = 125) was determined. Antibodies against the EPS of Penicillium digitatum, Mucor racemosus, Cladosporium cladosporioides, Fusarium moniliforme and Botrytis tulipae were found in relatively high amounts in all sera. No effect of age on antibodies present could be demonstrated. Antibodies against each of the EPS tested were only neutralized by the homologous EPS and by EPS of moulds belonging to the same genus or a taxonomically closely related genus. Antibodies against the EPS of P. digitatum were inhibited by methyl-beta-D-galactofuranoside, indicating that the galactofuranose part of this EPS is immunodominant.