Four patients with hematological malignancies, following bone marrow transplantation, who developed documented gram-negative [Klebsiella pneumoniae (2), Pseudomonas aeruginosa or Acinetobacter calcoaceticus] pneumonia during absolute neutropenia, were treated with a combination of antimicrobial therapy, granulocyte transfusions, and high-dose intravenous immunoglobulin. The patients recovered following this regimen, including 2 who had septic shock and respiratory failure, necessitating intubation and mechanical ventilation. These data suggest that therapy combining antimicrobial agents, granulocyte transfusions and opsonins may be effective in neutropenic patients who develop gram-negative pneumonia.