Deoxyribonuclease I (DNase I) was confirmed to be expressed in the human pituitary gland, particularly the anterior lobe, at levels comparable to those in the pancreas. The DNase I activity and the amount of gene transcript present in the pituitary glands of individuals aged from 1 month to 89 years was significantly age-dependent, with an abrupt elevation after the neonatal and prepubertal periods irrespective of gender, followed by a gradual age-dependent decline in males and a marked reduction in females in their postreproductive period. This DNase I age dependence in the pituitary gland was not present in the pancreas and serum. These observations suggest that tissue-specific up-regulation of DNase I gene expression in the pituitary gland occur, possibly at the onset of puberty.