The mechanical properties of 17 keloids in 9 patients before and during treatment with intralesional triamcinolone acetonide were studied using a recently developed noninvasive suction device for measuring skin elasticity in vivo. Each keloid was treated with intralesional injections of 10 mg/ml triamcinolone acetonide without local anaesthetic at intervals of 3 weeks. A total of four measurements per keloid were performed, before treatment and 3 weeks after the first, second and third treatments. The parameters used were: immediate distension (Ue), delayed distension (Uv), immediate retraction (Ur) and final distension (Uf). Relative parameters independent of skin thickness were calculated: Uv/Ue, the ratio between the viscous and the elastic deformation of the skin, and Ur/Uf, representing the ability of the skin to return to its initial position after deformation (biological elasticity). After three injections of triamcinolone acetonide a marked decrease in Uv/Ue and a less-pronounced increase in Ur/Uf compared with baseline values was observed. These findings indicate that the main effect of intralesional steroids on the connective tissue of keloids is a decrease in viscosity due to a loss of ground substance. This method provides a noninvasive quantitative assessment of the mechanical properties of scars and is well suited to comparative studies on the efficacy of various scar therapies.