An extract of tumour tissue from a patient with Kimura's disease was tested for eosinophil chemotactic activity using the Boyden chamber method. Eosinophil chemotactic activity was detected in the tissue extract, and after gel filtration maximum activity was found in the fraction with a molecular weight of approximately 1000 daltons. This factor may play a role in the tissue eosinophilia which occurs in Kimura's disease.