Chronic sun exposure and especially UVA wavelengths are responsible for long-term clinical skin changes such as photoageing and photocancers. The objectives of the present study were to analyse the contractile activity of fibroblasts irradiated with several doses of UVA and to evaluate the preventive, protective and restoring effects of a mixture of monomethylsilanetriol mannuronate and dimethylsilanediol salicylate. The forces generated by fibroblasts in tense collagen lattices were quantified using Glasbox device before and after UVA irradiation and the addition of a mixture of monomethylsilanetriol mannuronate and dimethylsilanediol salicylate. The production of collagen was also evaluated before and after irradiation and with and without the presence of a mixture of monomethylsilanetriol mannuronate and dimethylsilanediol salicylate. A dose of 3 J cm(-2) of UVA showed more than 50% of mortality in fibroblast population after 48 h and significant decreases in contractile forces developed by irradiated fibroblasts and collagen I production. One percentage of a mixture of monomethylsilanetriol mannuronate and dimethylsilanediol salicylate protected fibroblasts from UVA irradiation and made it possible to restore their capacity to the same level as fibroblasts that were not irradiated. It also tended to restore the capacity to synthesize collagen I. These results show that the use of the new device Glasbox makes it possible to evaluate a possible preventive and repairing effect of a cosmetic functional active on photoageing.