Abstract
Ultrastructural studies have been completed of the nature and time course of the destruction of guinea pig pancreatic B cells following the injection of streptozotocin. Hypertrophy of the Golgi complex was observed one hour after injection, while disruption and vesiculation of the membranes of the endoplasmic reticulum was seen three hours after a single intraperitoneal injection. Rupture of the B cell plasma membranes with consequent uncontrolled release of cytoplasmic contents occurred from four hours, and broken cells and debris were engulfed by macrophages from six hours after injection.