Drug therapy plays a significant role in causing neutropenia. The neutropenia may be immune mediated or due to direct inhibition of the bone marrow precursors. Recently, due to wide use of chemotherapy, febrile neutropenia has become a common and devastating problem. Neutropenia predisposes to many bacterial and fungal infections with organisms including gram negative bacilli such as E. coli, Klebsiella, and Pseudomonas; gram positive organisms such as Staphylococcus, Streptococcus viridans, and Enterococcus species; and fungi, like Candida and Aspergillus. In addition to the customary supportive care for neutropenic patients, therapy with recombinant human granulocyte colony-stimulating factor (rG-CSF) (filgrastim) has been shown to be beneficial. Filgrastim was a significant advance in the management of drug induced neutropenia in the past decade, but therapy with pegfilgrastim (a pegylated, long-acting form of filgrastim) ushers in the current decade. Pegfilgrastim (Neulasta) is administered as a single s.c. injection once per chemotherapy cycle. This results in fewer injections, fewer patient visits to the physician's office, and better patient compliance with therapy.