To improve the diagnosis of invasive aspergillosis (IA), we retrospectively compared competitive polymerase chain reaction (PCR) and sandwich ELISA for detection of serum galactomannan (GM) antigen. We studied 281 serum samples collected weekly during the period at risk for IA from 41 selected hematology patients. Twenty-two patients had confirmed, probable, or suspected IA, according to clinical and mycologic data. Fifteen of them had positive GM titers (87 samples) and 12 had positive PCRs (20 samples). Nineteen of the 20 PCR-positive samples were also GM-positive. Of the 19 patients without IA (83 samples), one had 3 GM-false-positive samples. Neither test anticipated the initiation of antifungal therapy on the basis of clinical suspicion. Both tests were more likely to be positive before death. This study suggests that PCR on serum samples is not more sensitive than GM detection. However, PCR can improve the specificity of the GM test. Together, these noninvasive tests should improve the diagnosis of IA.