SummaryRabbits were injected with 75Se-Methionine (75SeM) 4-8 hr after being subjected to a variety of experimental conditions: injection of ACTH, growth hormone, glucagon, adrenalin, endotoxin, turpentine, hydrocortisone and laparotomy. All of these experimental conditions except injection of glucagon were associated with increased incorporation of 75SeM into fibrinogen. Three patterns of incorporation of 75SeM into plasma proteins were recognized: 1. the pituitary pattern, which was observed in animals injected with ACTH, growth hormone or endotoxin, and which was characterized by increased incorporation of 75SeM only into fibrinogen and by a delayed incorporation of 75SeM into α2 and β1 globulins; 2. the tissue injury pattern, which was characterized by a markedly increased incorporation of 75SeM into fibrinogen and no alteration in incorporation of 75SeM into α2 or β1 globulins; and 3. the pharmacologic corticosteroid pattern, which was characterized by a moderately increased incorporation of 75SeM into fibrinogen and a strikingly increased incorporation of 75SeM into α2 and β1 globulins.