The utility of serum Aspergillus antigen in invasive aspergillosis was determined by identifying patients with >50 ng/mL Aspergillus carbohydrate antigen by ELISA. Patients were identified from a university hospital over a 65-month period. Nineteen patients with antigenemia had proven invasive aspergillosis, 16 had probable invasive aspergillosis, and 14 had an indeterminate diagnosis. There were 5 patients with false-positive results. Antigen levels were higher in disseminated infection than in invasive pulmonary aspergillosis (median levels, 500 and 121 ng/mL, respectively). Survival also correlated with antigenemia. Serial samples were obtained from 31 of 35 patients with proven or probable invasive aspergillosis. Fifteen of 19 patients with rising or persistent antigenemia died, whereas only 1 of 12 patients who cleared antigenemia died. Higher antigen levels were useful in predicting disseminated disease, and the course of antigenemia correlated with clinical outcome. Antigen detection may be a useful addition in the management of invasive aspergillosis.