We examined eosinophil-colony stimulating activity in blister fluid or serum obtained from patients with bullous pemphigoid using the methylcellulose semi-solid hematopoietic stem cell culture system, and demonstrated that the blister fluid of patients with bullous pemphigoid generated strong eosinophil-colony stimulating activity. This evidence suggests that eosinophil-colony stimulating activity in blister fluid probably influences the induction of eosinophilia in bullous pemphigoid.