Aspergillosis in cancer patients is a problem. Because not all patients can undergo invasive procedures, we sought other methods for diagnosis. We reviewed the data from all patients with acute nonlymphocytic leukemia treated at our center during a 3-year period. Of 125 patients, 18 had invasive aspergillosis (cases). Eleven patients had nose cultures growing Aspergillus flavus or A. fumigatus; 10 of these 11 had aspergillosis, whereas only eight of 114 without such nose cultures had invasive disease (P less than 0.000001). Thus, A. flavus on nose culture appears "predictive" for aspergillosis. Absence of such a culture does not preclude infection. Of 125 patients, 61 had sterile nose culture(s) and 14 of the 18 cases had such a sterile nose culture. Only four of the 64 patients without sterile nose cultures developed aspergillosis (P less than 0.008), suggesting a relation between sterile nose culture and aspergillosis. Carbenicillin was used for a longer period among cases and patients with predictive nose cultures than among patients without aspergillosis. These data may help identify patients at risk of aspergillosis and help determine antifungal therapy when invasive procedures are contraindicated.