Acute effect of streptozotocin-induced diabetes on several parameters of glucose metabolism was investigated in thymus lymphocytes (thymocytes). The cells from diabetics rats accumulated in vitro about 2-fold more fructose 2,6-bisphosphate (Fru-2, 6-P 2 ) in the presence of increasing glucose concentration than cells from normal rats. An increased production of lactate was also observed. Phosphofructokinase-1 (PKF-1) and phosphofructokinase-2 (PKF-2) activities were enhanced in cells from diabetic rats compared with those from normal rats. [U- 1 4 C] glucose incorporation into glycogen was also increased in cells from diabetic rats and the 1 4 CO 2 liberation was lesser than in cells from normal animals. From these data it may be concluded that the response of thymocytes to streptozotocin-induced diabetes is similar to that observed in other extrahepatic tissues.