The aim of our study was to evaluate the effect of aging and postmenopausal hypoestrogenism on skin collagen content. Thirty-two women (mean age 48.78 +/- 9.86; year +/- S.D., range 28-68), 14 in premenopause and 18 in postmenopause, underwent skin biopsies performed during laparotomic operation. The amount of collagen type I, III and type III/type I ratio was evaluated by immunohistochemistry and computerised image analysis, and was related to age and years of postmenopause. In the postmenopausal patients, a significant (P < 0.01) decrease of percentage of skin collagen type I, type III and type III/type I ratio was observed in comparison to premenopausal women. The percentages of collagen type I, type III and type III/I ratio of all patients studied was significantly (P < 0.01) correlated with chronological age (r = 0.88, 0.89 and 0.61, respectively). Considering only postmenopausal subjects, the correlation with chronological age was significant (P < 0.01) for collagen type I and type III of postmenopausal women (r = 0.59, r = 0.64, respectively), but not for the type III/I ratio (r = 0.37, P = 0.131). The percentages of collagen type I, type III and type III/I ratio of postmenopausal women showed a significant (P < 0.01) inverse correlation with years of postmenopause (r = 0.76, 0.73 and 0.73, respectively). Our data suggest that the decrease of skin collagen is an estrogen-related phenomenon.