The aim of the study was to evaluate the relation between the activity of collagenase in the subchondral bone of the femoral head and the age of patients with hip osteoarthritis. Thirty-two patients were enrolled into the study. The mean age was 66 (range from 37 to 80 years). Bone samples of the femoral head were harvested during total hip replacement. The activity of collagenase was measured through spectrofluorimetry. We found statistically a significant correlation between collagenase activity in the bone and age. The mean activity of collagenase in younger patients (37-68 years) was 64.17 IU/microg. In older patients (69-80 years), the mean collagenase activity was 52.26 IU/microg. In patients with hip osteoarthritis the activity of collagenase in the subchondral bone of the femoral head tended to decrease with an increase in age.