Diabetes mellitus is the important health problem in the developed countries. Type 1 diabetes mellitus and its complications can be studied either on genetic models or it can be induced postnatally. One of the most frequently used postnatal models is the experimental diabetes induced by streptozotocin (STZ). This article presents an overview of STZ use in small and bigger experimental animals and their sensitivity to the diabetogenic effect of this drug. Some new aspects of the long-term STZ diabetes in albino rats (12 months) are provided.