Immunohistochemical study combined with morphometry was carried out to examine the expression of cyclooxygenase-2 (COX-2) using 60 human skin wounds of different ages: group I, 0-4 h (n = 11); II, 8 h-2 days (n = 21); III, 3-9 days (n = 14); and IV, 12-21 days (n = 14). In wound specimens aged 2 h to 2 days, anti-myeloperoxidase-positive neutrophils observed at the wound site expressed immunopositive reaction to COX-2. In wound specimens of more than 3 days, CD68-positive macrophages as well as neutrophils were positively immunostained with anti-COX-2. In group II, all 21 wound samples had COX-2-positive ratios of >40 %, and 15 out of them showed >50 %. In group III, only three wound samples with the postinfliction intervals of 3 days showed positive ratios of 40-50 % and the remaining 11 cases less than 40 %. In groups I and IV, all 25 wound specimens had COX-2-positive ratio of <40 %. With regard to the practical applicability with forensic safety, these observations suggested that a COX-2-positive ratio of >40 % indicated a wound age of 8 h to 3 days. Moreover, COX-2-positive ratios, considerably exceeding a ratio of 50 %, indicate a wound age of 8 h to 2 days. Collectively, COX-2 would be a useful marker for the determination of early wound age.