A nucleoside diphosphatase with activity restricted to the Golgi apparatus was demonstrated at pH 9.2 in various cell types in rabbit, guinea pig and dog. This enzyme hydrolyzed the diphosphates of uridine, guanosine, cytidine and inosine as well as uridine triphosphate. It had histochemical properties which distinguish it from the golgi nucleoside diphosphatase previously visualized by other workers at pH 6.7.