The diagnosis and successful control of systemic Aspergillus niger infection in 2 adult patients with acute leukemia is reported. During induction therapy, the first patient developed pulmonary infiltrates, skin lesions and abnormal liver function tests. Aspergillus niger was found on skin and liver biopsy. This patient was successfully treated with Amphotericin B and granulocyte transfusions and he remains in remission. The second patient developed a pneumonitis and adynamic ileus with positive sputum and stool cultures for Aspergillus niger. The infection only responded to Amphotericin B and granulocyte transfusions and the leukemia to cytoreductive chemotherapy. The patient later relapsed and died after a febrile illness. Fungi morphologically consistent with Aspergillus were found in the liver at autopsy. Infection with A. niger is rare even in this patient population; however fungal infections have become an increasing problem. The need for a high index of suspicion, especially when an infection is unresponsive to antibacterial antibiotics, the various diagnostic tools, and the need for aggressive therapy are stressed. Amphotericin B is the chemotherapy of choice but may be insufficient in a severely neutropenic host where the simultaneous use of granulocyte transfusions might be lifesaving.