We studied by ultramicroscopy the tissue response after mesh hernia repair. 11 patients, bearing dacron mesh from 7 days to 9 years, were biopsied during later operations. There were two groups of patients: 6 with a normal tissue response and 5 with rejection of the mesh. We observed that mesh repair was characterised by development of a foreign-body giant cell layer around the fibres, the presence of macrophages in an intermediate layer and fibroblasts in the outer layer. Collagen fibres and bundles ran between the giant cells and the host tissues. When the mesh was rejected, there were no chronic inflammatory cells and collagen bundles were reabsorbed. In the peripheral areas where the mesh-integrated tissue still persisted, there was a considerable reduction in the numbers of the giant cells and there were red blood cells and acute inflammatory cells instead of macrophages and epithelioid cells. Collagen was reduced to fibrils. From our results, mesh-tissue repair seems to be a dynamic and unstable process characterised by chronic inflammation and continuous collagen maturation. During the development, the tissue response to the mesh, as with any inflammatory condition, makes colorisation by hematogenic bacteria easier. Infection can destroy the capsule around the mesh and causes its rejection.