Sputa from patients with respiratory infections by nontypable Haemophilus influenzae (H. influenzae) were investigated by electron microscopy. The cell wall of H. influenzae appeared wavy and nonwavy. In the cell wall the peptidoglycan layer was ill-defined. These patients had adequate IgG response in the serum against H. influenzae. However neither capsule nor fimbriae were found. Different stages of phagocytosis and destruction of the bacteria by polymorphonuclear neutrophils (PMN) were observed. PMNs were also found to phagocytose the debris. Evidences were found that the debris is formed mainly by the destruction of polymorphonuclear neutrophil. Extracellular lysosomes were also observed, which may have a role in destruction of both bacteria and host tissue. It was concluded that nontypable H. influenzae are nonfimbriated and noncapsulated during infection. Debris are the end product of PMN destruction, and phagocytosis of debris by PMNs has a role in the pathogenesis of chronic respiratory diseases.