Aging is associated with decreased reparative ability of the gastric mucosa. Our recent data suggest a role for epidermal growth factor receptor (EGFR) in the mucosal reparative processes. Thus we examined changes in EGFR tyrosine kinase activity as well as expression and subcellular localization of EGFR and its ligand transforming growth factor- (TGF-) in the gastric mucosa of young (4-mo-old) and aged (24-mo-old) Fischer 344 male rats during the early reparative phase after acute injury induced by 2 M NaCl. Within 240 min of injury, significant epithelial restitution was observed in the gastric mucosa of young but not of aged rats. Expansion of the neck region and initiation of foveolar cell migration could be seen within 45 min of injury in young rats but not until 90 min in aged rats. In young rats mucosal EGFR tyrosine kinase activity increased at 45 min after injury and subsequently fell to basal levels. Mucosal EGFR mRNA increased throughout the reparative phase as did content of the EGFR ligand TGF-. In contrast, although the basal tyrosine kinase activity and levels of EGFR mRNA and TGF- were elevated in the gastric mucosa of aged rats, injury did not cause increases in these parameters. Immunofluorescent localization suggests that internalization and/or degradation of EGFR may be higher in aged than in young rats. We suggest that diminished induction of EGFR tyrosine kinase activity and increased EGFR internalization after injury may in part be responsible for the age-related decrease in the reparative capacity of the gastric mucosa.