The behaviour, under burn scars , of three different alloplastic materials, silicone, Medpor and Proplast, was compared in an animal model. A standard burn wound was created in rats, and 3 months later silicone, medpor and proplast alloplasts were placed under the burn scar. The rats were followed for another 3 months and ulceration and/or alloplast exposure rates were evaluated. At the end of this period specimens were examined histologically for the thickness of the fibrous capsule around the implant, thickness of the overlying tissue, tissue ingrowth and vascularization of the implants. Ulceration and exposure occurred in 2 of the 12 Medpor, 2 of the 12 Proplast and none of the 12 silicone implants. Fibrous capsule was significantly thicker around the silicone implants. Tissue ingrowth and vascularization were most prominent in Medpor implants while thickness of the overlying tissue was maximum in Proplast implants. These findings suggest that complications with silicone implants may be less than with other porous implants when used under burn scarred tissue. (C) 1997 Elsevier Science Ltd for ISBI.