Antigenic extracellular polysaccharides (EPS) were produced by Penicillium digitatum and P. aurantiogriseum under various conditions, including different carbon and nitrogen sources, glucose concentrations and incubation periods. With lactate as carbon source no antigenic EPS was produced. EPS consisted mainly of glucose, mannose and galactose. Differences were seen in the monosaccharide composition. The amount of glucose in the medium (1–30 g/l) influenced growth and the production of antigenic EPS moderately. The antigenicity of P. aurantiogriseum EPS, but not that of P. digitatum, decreased with prolonged incubation. P. aurantiogriseum, but not P. digitatum, grew well with nitrate as the nitrogen source.