Aging of the human skin is a complex process that consists of chronological and extrinsic aging; the latter caused mainly by exposure to ultraviolet radiation. Here we present studies in which we have used proteomic profiling technologies and 2D PAGE database resources to identify proteins whose expression is deregulated in the epidermis of the elderly. Fresh punch biopsies from the forearm of 20 pairs of young and old donors (21-30 and 75-92 years old) were dissected to yield an epidermal fraction that consisted mainly of differentiated cells. One to two mm³ epidermal pieces were labeled with [³⁵S]methionine for 18 h, lyzed and subjected to 2D PAGE and phosphorimage autoradiography. Proteins were identified by matching the gels with the master 2D-gel image of human keratinocytes (http://proteomics.cancer.dk). In selected cases 2D PAGE immunoblotting and/or mass spectrometry confirmed the identity. Quantitative analysis of 172 well-focused and abundant polypeptides showed that the level of most proteins (148) remains unaffected by the aging process. Twenty-two proteins were consistently deregulated by a factor of 1.5 or more across the 20 sample pairs. Among these we identified a group of six polypeptides (Mx-A, Manganese superoxide dismutase, tryptophanyl tRNA synthetase, phosphatidylinositol 3-kinase, and proteasomal proteins PA 28 - and SSP 0107), that is induced by INF- in primary human keratinocytes, and that represents a specific protein signature for the effect of this cytokine. Changes in the expression of the eukaryotic initiation factor 5A, NM23 H2, cyclophilin A, HSP60, annexin I, and plasminogen activator inhibitor 2 were also observed. Two proteins exhibited irregular behavior from individual to individual. Besides arguing for a role of INF- in the aging process, the biological activities associated with the deregulated proteins support the contention that aging is linked with increased oxidative stress that could lead to apoptosis in vivo.