High incidence of aspergillosis on transplant units or hematological wards without HEPA air conditioning during periods of demolishing or construction has been reported by several investigators. Here we report monitoring of fungal air contamination during a period of construction on a stem cell transplantation ward using the gravity air-setting plate (GASP) method. Fungal air contamination in HEPA-conditioned patient rooms was constantly low, independent from construction activity. Outside of the patient rooms at the ward's corridor, the fungal load was significantly higher with some peak values. Outside the transplant unit measures of construction led to a significant increase of fungal spore concentration in air. Transplant activity was not reduced during construction and patients were nursed strictly under HEPA conditions. Patients were monitored prospectively for incidence of infections since 1990 and data of patients grafted during construction (n = 28) were compared to those grafted outside building activity (n = 652). An increase of aspergillosis during construction could be clearly excluded. It can be concluded: Nursing of patients undergoing stem cell transplantation in HEPA-conditioned rooms is an effective protection against acquisition of aspergillus-infection, even under environmental conditions with increased air contamination by conidia. The gravity air-setting plate (GASP) method is not expensive and easy to use and allows reliable and quantitative aerobiological spore monitoring.