The healing process after inflicting silver nitrate burns, a type of injury in which a heavy loss of body wall tissues occurs, was studied in Hirudo medicinalis. Silver solution penetrates the body wall and silver precipitates in the tissues during infiltration. Vasocentral cells, do not penetrate the impregnated zone but accumulate just below it to form a pseudoblastema. The impregnated zone splits off entirely, leaving an area covered by pseudoblastema cells on the leech surface, which is progressively reepithelialized. There is no regeneration of the lost body region, and although some connective tissue matrix may be produced by pseudoblastema cells, there is no significant regeneration of the connective tissue and nor the muscular fibers of the body wall, resting an evident depression in the damaged zone. The amount of affected tissue, and possibly the inability of vasocentral cells to reach the infiltrated tissues are determinant factors in the development of the splitting process. Copyright 1999 Academic Press.