We report a Churg-Strauss syndrome case complicated by Giardia Lamblia infection which increased markedly the number of blood eosinophils with appearance of eosinophils able to form rosettes with unsensitized sheep red blood cells. Metronidazolo therapy reduces markedly the blood hypereosinophilia. The strong relationship between blood hypereosinophilia and Giardia Lamblia in this patient, suggests that there is an interaction between different eosinophilopoietic stimuli.