Guinea pigs actively sensitized with chicken egg albumin, sheep erythrocytes or rat erythrocytes combined with paraffin oil adjuvants, reacted to the subcutaneous injection of the homologous antigen with a protracted systemic anaphylactic shock. The symptoms of systemic protracted shock followed this sequence: Pruritus, dyspnea, erection of the papillae of the skin, hypothermia, collapse. The temperature may fall to 33–35°C after an hour. Death may occur from 1–30 hr after the eliciting dose. At necropsy, the most striking observation was stasis and/or hemorrhages of the stomach and intestinal walls. Guinea pigs passively sensitized with rabbit or guinea pig antibody 19–20 hr prior to subcutaneous challenge died in acute or protracted shock, depending upon the amount of passively transferred antiserum. Within certain limits the speed of death increases with decreases in the quantity of antibody injected indicating that “excess” antiserum presumably free in the circulation, acts to prolong the syndrome. Actively sensitized guinea pigs immunized without paraffin oil adjuvants suffered a more acute shock after subcutaneous challenge than did animals immunized with incomplete adjuvants. Pyribenzamine and Phenergan injected intraperitoneally in actively or passively sensitized guinea pigs prior to a subcutaneous eliciting injection protected against the respiratory symptoms. Nevertheless, a severe or lethal protracted anaphylactic shock occurred in antihistamine treated animals. In these guinea pigs, necropsy revealed little if any lung involvement.