Problems of classification of certain growth processes were discussed using jugular body tumors to find out cytological criteria for characterizing growth traits. For this purpose light microscopical (9 cases), electron microscopical (6 cases) and enzyme histochemical investigations (3 cases) were performed. For comparison 4 carotid body tumors were examined. We are inclined to assume a neoplastic nature. An explanation as hyperplastic proliferation is refuted because a remarkable cellular variation in size and form, only sparse nerve fibers and lacking synaptic contacts, because submicroscopical features and because the clinical picture and course of the disease. It is pointed to the origin of the tumor cells from rudimentary endocrine-like cells occurring in the glomus jugulare-tympanicum in analogy to other neoplasias. The clinical symptoms, the course and the pathologic anatomical pattern suggest an interpretation of jugular body tumors as potential malignant growths.