Many tissues are constantly exposed to mechanical stress, e.g. shear stress in vascular endothelium, compression forces in cartilage or tensile strain in the skin. Dermal fibroblasts can differentiate into contractile myofibroblasts in a process requiring the presence of TGFβ1 in addition to mechanical load. We aimed at investigating the effect of cyclic mechanical strain on dermal fibroblasts grown in a three-dimensional environment. Therefore, murine dermal fibroblasts were cultured in collagen gels and subjected to cyclic tension at a frequency of 0.1 Hz (6 cycles/min) with a maximal increase in surface area of 10 % for 24 h. This treatment resulted in a significant increase in active TGFβ1 levels, leaving the amount of total TGFβ1 unaffected. TGFβ1 activation led to pSMAD2-mediated transcriptional elevation of downstream mediators, such as CTGF, and an auto-induction of TGFβ1, respectively.