In order to determine the morphological characteristics of certain vascular and glomerular lesions and the correlation between them, we attempted three-dimensional observation using serial sections of an autopsy kidney, from a patient with panarteritis nodosa in the acute phase. Fibrinoid necrotizing vasculitis spread from arcuate arteries to arterioles in a segmental, eccentric pattern, especially occurring at bifurcations. Segmental arteriolitis often originated in extraglomerular capsular arteriole and spread into the intraglomerular capsular arteriole and glomerular capillaries, directly leading to necrotizing glomerulitis. Some of the glomerulitis connected directly with extracapsular arteriolitis was segmental and eccentric in distribution. Most of the glomerulitis had a tendency to originate in the hilar arteriole, which was near bifurcations between the arteriole and glomerular capillaries. Segmental glomerulitis was found to consist of four elements: glomerular tuft necrosis with fibrin exudation, crescents, rupture or dissolution of Bowman's capsule, and pericapsulitis. It is suggested that the segmental inflammatory attacks, repeated more than twice, give rise to widespread and almost global necrotizing glomerulitis.