In a study to determine the value of antigen and antibody detection in the serological diagnosis of invasive aspergillosis in patients with hematological malignancies, 436 sequential serum samples from 79 neutropenic patients were tested. Circulating galactomannan antigen was detected with a latex agglutination method (Pastorex Aspergillus) and antibody to Aspergillus fumigatus with an immunodiffusion test on agar gel. Among the 79 patients 18 cases of invasive aspergillosis were detected (4 proven, 6 highly probable, 3 probable, 5 suspected). Antigen was detected in 7 of these 18 patients. The sensitivity of the antigen test was 38.8% and the specificity 95%. The antibody test showed 55.5% sensitivity and 100% specificity. In this study the antigen test was less sensitive than previously reported but highly specific and might serve as a supplementary diagnostic test.