Diabetic animals have contributed to the understanding of the causes, consequences and treatment of diabetes. There are different ways to induce experimental diabetes, chemically induced experimental diabetes has been widely used. Alloxan and streptozotocin are the chemicals most used. A comparative study of these two agents was performed in order to determine their effectiveness. Twenty−seven Sprague−Dawley male adult rats were intraperitoneally(i.p.) injected with 120mg/kg BW of alloxan(AL) and 27 with 60mg/kg BW of streptozotocin(STZ). Levels of glucose, insulin, triglycerides and total cholesterol were determined at different times after the i.p. injection. The effect of the two chemicals on the Langerhans’ islets was histochemically demonstrated. The reversibility of the diabetic state, 20 days after the i.p. injection of AL, was demonstrated by the recovery of insulin levels, reduction of the glucose and triglycerides concentration and by positive anti−insulin antibodies reaction in the pancreatic tissue. STZ proved to induce a more stable and permanent diabetic state.