ABSTRACT The aim of this study was to quantify the effectiveness of intradermal application of autologous fibroblasts on lean tissue structures. The histological sections of the skin were analysed and evaluated for the expansion potential of autologous fibroblasts in the control skin patch area and the nearby pre-treated skin patch into which we had injected expanded autologous fibroblasts nine month earlier. The results show that the pre-injection of fibroblasts into the dermis leads to a long-term rejuvenation of the skin, as evaluated from the histological appearance and from the significantly increased density of fibroblasts in the pre-injected skin vs. controls, from around 60% to over 80%, determined as the percent of lean tissue by a novel image analysis approach. Interestingly, the rate of the in vitro fibroblast expansion from the pre-injected area of the skin was reduced in comparison with the controls, consistent with the view that fibroblasts exhibit a limited cell-division potential and that fibroblasts from the pre-injected skin already experienced expansion nine month earlier prior to the injection into the skin. We conclude that autologous fibroblast application results in a significant long-term augmentation of the lean tissue elements of the skin