A Ei-month-old Hispanic boy had a diffuse eruption and massive periphe
ral eosinophilia, Mastocytosis was diagnosed by skin biopsy and Giemsa
stain, Other causes of eosinophilia were ruled out by bone marrow exa
mination and negative cultures, The patient's course improved with ant
ihistamines and the removal of mast cell degranulating agents, Clinici
ans need to be aware that mastocytosis should be considered in the dif
ferential diagnosis of eosinophilia.