The assimilation characteristics of absorbable bovine fibrin implants in an experimental situation are described, and the effect of delaying absorption with formaldehyde treatment is demonstrated. Essentially, in vivo in the rat, Biethium fibrin implants are absorbed in approximately four to eight weeks because of the polymorphonuclear leukocyte digestion. An indication of the clinical uses in stress incontinence and hemorrhage of the liver are given, together with a look at the future of some of the other areas in which this absorbable, biologic plastic may fit into the surgeon's armamentarium to replace deficient or destroyed tissue.