Histological and ultrastructural studies of juxtaglomerular cells (JGC) were performed in a patient with pseudo-Bartter's syndrome due to furosemide abuse. The biopsy done before the treatment revealed a large number of secretory granules and mitochondria, dilated rough endoplasmic reticulum and a well-developed Golgi apparatus in JGC. The JGC granules, some of which contained crystalloid structures showed various shapes and sizes. In the biopsy carried out after the cessation of furosemide intake, these morphological changes were markedly improved with a reduced activity of the renin-angiotensin system. The characteristic changes of JGC may be valuable in determing the functional and morphological interrelations of this disorder.