In a group of 40 cerebral contusions with a different period of survival by histological and histochemical methods changes in the contusion foci and their surroundings were assessed. The authors compared their own findings with those of other authors. Their finding of leucostasis and incipient leucodiapedesis was found in cerebral contusions with 7 hours survival. A more marked incidence of leucocytes near the contusion was in cases with a survival of 30 hours. A readily apparent gliomensenchymal reaction near the contusion focus was found in patients who survived the injury for eight days. In the glial elements acid phosphatase and no-specific esterase activity was detected. In contusion of the frontal lobe with a 13-day survival considerable cellulization and increase in the amount of capillaries was found near the contusion focus. In survival of contusion of the frontal lobe for 28 days the glial elements with an acid phosphatase and non-specific esterase activity form a margin round the contusion focus. Even in contusion of the frontal lobe with 5-month survival numerous granular cells were found in the neighbouring area. The results obtained by the authors are not always consistent with those of others. The data of other authors frequently vary too. Therefore it is important to be careful about estimates of the age of cerebral contusions and in particular in cerebral contusions with longer survival the estimate of the age of the injury is only approximate.