A histological and ultrastructural survey of the early effects of cadmium chloride on the testis of the gerbil, Meriones unguiculatus, was performed. Within three hours after treatment, evidence of cadmium injury to the interstitial vascular bed is histologically apparent. By four hours, marked edema and some microhemorrhaging are noted. Ultrastructural changes consisting of extensive pinocytotic activity along the distal borders of endothelial and perivascular cells, some abnormal vacuolization and distention of endoplasmic reticulum, and loosened endothelial desmosome junctional complexes are noted within three hours. Cadmium injury to the testis is characterized by a marked increase in vascular permeability. These observations are discussed in relation to the biochemical mechanisms involved in this pathogenesis.