IgE antibodies to Pityrosporum orbiculare and 16 other species of fungi were measured with the radioallergosorbent test (RAST) in sera of 131 children. The children were 7-18 years old, suffered from atopic diseases and showed a varied allergic profile on a skin prick test (SPT). IgE antibodies to P. orbiculare were found in the sera of 26 of the 131 children. A higher proportion of the P. orbiculare RAST positive children than of the negative ones had current eczema (p less than 0.0001). In a stepwise logistic regression analysis of SPT and RAST data, the occurrence of serum IgE antibodies to P. orbiculare had the highest explanatory value for current eczema. Ten of 15 children with current atopic eczema and total serum IgE of greater than 500 kU/l had serum IgE antibodies to P. orbiculare. Twenty-four of the 26 P. orbiculare RAST positive children harboured serum IgE antibodies to other fungi. The strong relationship between atopic eczema and the occurrence of IgE antibodies to P. orbiculare indicates that these antibodies may be pathogenetically important in at least some patients with atopic eczema and this gives another dimension to this common skin disease.