Irritant effects and cytotoxicity of three different products based on collagen were investigated: a sponge formulation and a thin film composed by Type I collagen from bovine Achille's tendon, and a membrane prepared from bovine derma. The test system was a three-dimensional human skin model, developed by Advanced Tissue Science, La Jolla, CA, USA. Squares of dermal tissue (11 x 11 mm) were cultured in suitable media and exposed to the products under study. Dimethyl sulphoxide was used as the chemical control of tissue responsiveness to irritating substances. After 24 and 48 h the prostaglandin E2 (PGE2) concentration and the lactate dehydrogenase (LDH) activity in the culture medium were measured, as indexes of early inflammatory response and cell membrane breakdown, respectively. In addition, cell morphology was examined by light microscopy. The highest PGE2 concentrations were observed after cell exposure to the collagen sponges. The intensity of the inflammatory response changed accordingly to the collagen dose in use. However, it was never followed by an increased rate of cell death, as revealed by LDH activity measurement and microscopy. These findings suggest that hydrolysis of exogenous collagen starts shortly after it is kept in contact with tissues and evokes a local inflammatory response whose intensity depends on the pharmaceutical formulation in use.