Kawasaki disease is an acute vasculitic illness of childhood associated with significant morbidity and mortality. A cellular based enzyme linked immunosorbent assay (ELISA) was used to demonstrate the presence of antiendothelial cell antibodies in sera from children with Kawasaki disease. Twenty one of 32 patients with Kawasaki disease had raised IgM antibody titres and four had raised IgG antiendothelial antibody titres. There was a significant difference in the IgM antiendothelial cell antibody titres when comparing the patients with normals and febrile controls. The antibody titre paralleled the disease activity in patients studied serially. There was no relative increase in binding of antiendothelial cell antibodies after cytokine stimulation. These findings may be of importance in further research into the understanding of mechanisms involved in this and other forms of vasculitis in man.