Abstract Cracked building elements are increasingly being repaired by the injection of reactive resins. This includes the nonpositive injection with epoxy resins for the protection of corrosion of the reinforcement and to restore simultaneous ly the stiffness of an uncracked construction by glueing the crack surfaces. In the tests the influence of different loading and climatic conditions on the morphology of the interface between several epoxy systems and crack surfaces was investigated by means of scanning electron microscopy. The bond strength between resin and concrete was measured in mechanical tests of concrete elements which were injec ted under dry and wet conditioning. The results of further tests with water-modified epoxy systems showed the influ ence of different water contents on the bond behaviour of the reactive resins. Keywords: Interface, Morphology, Bond Strength, Crack In jection, Reactive Resin, Adhesive Behaviour.