A study was made of the time course of development of alloxan diabetes in mature male Wistar and random bred rats for a quantitative analysis of responses to the administration of a diabetogenic dose of the drug. Proceeding from the animals' death, a decrease in body mass, water consumption, the blood level of glucose and GTT results the animals were divided into 3 groups depending on the gravity of alloxan diabetes. In Wistar rats acute, obvious and latent types of diabetes developed in 35, 35, and 30 % respectively. Rats with obvious diabetes were characterized by a significant decrease in the IRI level in the plasma 3-8 weeks after drug administration. In rats with latent diabetes the IRI level in the plasma on the 3rd week showed a tendency to a decrease and exceeded control values in 8 weeks. In random bred rats acute, obvious and latent types of diabetes were noted in 76, 12, and 12 % respectively. The results have shown that the division of animals into the groups with a different degree of gravity of alloxan diabetes can express quantitative assessment of the sensitivity of a population in question to the diabetogenic action of alloxan.