Lungs from 26 cases were examined in which blood was present as a result of a gunshot wound, a stab wound, or aspiration. Signs of vitality and of a time-dependent reaction sequence were evaluated to determine survival time. Only those morphologic criteria were considered that could be obtained on paraffin sections. In addition to H & E staining, siderin was identified with the Prussian blue reaction and the activities were determined of tartrate-resistant acid phosphatase, as macrophage marker, and naphthol AS-D chloracetate esterase, as granulocyte marker. The following criteria were evaluated: granulocyte emigration, erythrocyte adherence to the surface of macrophages, macrophage ingestion of erythrocytes, and determination of siderin as indicator of intracellular erythrocyte digestion. Adherence was also observed in those cases that did not survive. The initial sign of vitality was granulocyte emigration, which was observed for the first time after a survival time of 5 min. Erythrophages were found after a survival time of 30 min at least, siderophages after 17 h at the earliest. Literature dealing with vitality and age determination, as well as the pathogenesis of the reaction sequence, is discussed.