The hematopoietic growth factors are under investigation for the treatment of patients with chemotherapy-induced bone marrow suppression. One such trial at the University of California, Los Angeles involves chemotherapy with or without granulocyte colony-stimulating factor (G-CSF) in patients with small cell lung cancer. The authors report a case of a patient who had bullous pyoderma gangrenosum at the site of previous eczema during treatment with G-CSF. The lesions resolved promptly when the drug was discontinued. Other investigators have recently reported inflammatory complications of G-CSF and granulocyte-macrophage colony-stimulating factor (GM-CSF) but this is the first case report of biopsy-proven neutrophilic dermatosis associated with administration of a hematopoietic growth factor. Patients should be monitored for development of inflammatory processes during G-CSF therapy and this therapy should be given with caution to those patients with existing inflammatory conditions.