It is generally held that leukocytes are found within bruised subcutaneous tissues within 4-12 h of injury as part of a standard cellular response to trauma. As a corollary, the absence of leukocytes is often cited as evidence of more recent injury. To investigate how long after injury it may be before a leukocyte response occurs selected bruises from three children aged 27, 11, and 3 months, respectively, were examined microscopically. All of the children had sustained lethal head trauma, with survival on life-support equipment for some time in hospital, and with bruises of at least 24-h duration confirmed by medical evaluation (at 30, 44, and 79 h from the time of initial medical evaluation to death). Histologic examination of selected lesions in all three cases revealed extravasation of red blood cells within subcutaneous tissues, but no leukocyte infiltration or other cellular reaction. Other bruises in these children exhibited a standard inflammatory response. This study has shown that selected bruises in three children were present for at least 30 h without a leukocyte infiltrate. Caution should, therefore, be exercised in assigning too rigid a time course to bruising in infants and young children based on a lack of a vital reaction, as the absence of leukocytes within soft tissues of bruised skin in these cases may not necessarily indicate that the injuries are recent. Variability in tissue response may also occur in different bruises in the same individual. Whether severe craniocerebral trauma played a role in delaying the cellular response in these particular injuries is unclear.