Summary: A significant drop in blood-platelets is a constant finding in anaphylactic shock in the monkey. It does not occur in nonsensitized controls, occurs slightly and irregularly in sensitized animals showing no clinical shock, and is not observed in animals shocked with histamine. A profound leukopenia (essentially granulopenia) with a secondary leukocytosis is a constant finding in anaphylactic shock in the monkey. Such changes are also observed in some animals exhibiting no clinical symptoms of shock. There is a significant rise in plasma potassium in monkeys showing severe anaphylactic shock. This is of lesser degree than that observed in other species.