In maintaining the rat, the collagen dressings, Aviderm Amine and Aviderm, are as effective as skin in low bacterial levels in contaminated surgical wounds. In the scald-burn wound in the rat the effect of skin dressing is confirmed. Also, 48 h after collagen dressing in the wound the bacterial contamination was the same as that seen under autograft dressings. We have elsewhere suggested that skin and some other dressings modify the local host defense by their effect on the accumulated white blood cells. We believe that collagen, as well as some synthetics, can alter the local environment permitting the destruction of invading bacteria by the accumulated white blood cells.