This study of wound repair, inflammation and connective tissue is designed to further clarify the roles played by the leukocytes, thrombocytes, and plasma constituents during the different phases of wound repair in relation to re-endothelialization, stimulation of fibroblast migration and their proliferation, and the synthesis of connective tissue matrix constitutents. It also proposes to further define the components of the elastic fiber and to study their formation in vivo and in vitro. The goals have been to isolate, identify, and characterize the factor elaborated by platelets during the "platelet release reaction." It has been demonstrated that macrophages appear to play a principal role in stimulating fibroblast proliferation in vivo, since it has been possible to eliminate the bulk of this activity by combined use of antimacrophage serum locally in wounds together with a monocytopenia produced by hydrocortisone. The activation of macrophages with latex particles or opsonized erythrocytes has been demonstrated to result in release into the medium of a factor that stimulates fibroblasts to proliferate in cell culture. The studies of the various mitogenic factors derived from platelets and macrophages will be of great importance, if the role played by the various inflammatory cells in wound repair, particularly in terms of its stimulus and its resolution, is to be understood. BIBLIOGRAPHIC REFERENCES: Narayanan, S., Sandberg, L.B., Ross, R., Layman, D. The Smooth Muscle Cell III. Elastin Synthesis in Arterial Smooth Muscle Cell Culture, J. Cell Biology, 68:411-419, 1976. Leibovich, J.J. and Ross, R. A Macrophage Dependent Factor that Stimulates the Proliferation of Fibroblasts In Vitro, Amer. J. Path, 84:501-513, 1976.