Serum tryptase levels in patients with marked eosinophilia due to HES, other idiopathic eosinophilic disorders, parasitic helminth infection, and systemic mastocytosis with eosinophilia. Each symbol represents the first serum tryptase value available for an individual patient. The median serum tryptase level for each group is indicated by a horizontal bar. The shaded box represents the normal range. Elevated serum tryptase levels are present in a subset of patients with HES and one patient with idiopathic eosinophilic gastroenteritis. As expected, the 3 patients with systemic mastocytosis have markedly elevated levels.