Four commercially available Aspergillus fumigatus antigens were compared in an IgG enzyme linked immunosorbent assay by testing multiple sera from 19 patients who had received renal and hepatic allografts and who had histologically confirmed invasive aspergillosis. Raised antibody levels were found in 16 of the 19 patients. More antibody responses were detected by culture filtrate antigens, but somatic antigens often detected antibodies sooner. When antibodies to Aspergillus antigens were present before transplantation the onset of fatal disseminated infection was earlier. Antibody levels often fell to within the normal range, even in cases of fulminant disseminated infection. Repeated serology was essential for detection of an antibody response.