During a three-year period nine patients with haematological diseases after myeloablative chemotherapy died from invasive fungal infections caused by Aspergillus terreus. The hospital inanimate environment was monitored and A. terreus was cultured from potted plants in the vicinity of the patients. The patients (N = 14) and the environmental isolates (N = 2) were fingerprinted by RAPD-PCR with four different primers. Based on RAPD patterns the patients' isolates were differentiated into five different types; the environmental isolates represented two types. The isolates of four patients were identical to those found in the environment. Five additional patients were infected by RAPD types not found in the environment. One patient was infected with two different types. The data indicate a hospital-acquired infection in many of the patients and underline the need for careful environmental monitoring of units in which high-risk patients are housed.