Enhanced glucose transport is one of the earliest responses of the thymocyte to concanavalin-A, a growth stimulant in this cell. Reduced glucose transport is one of the earliest responses of this cell to glucocorticoids, which inhibit growth. The association between growth and glucose transport is seen in cultured fibroblasts subjected to a variety of growth-affecting agents including sarcoma-virus transformation. Our objectives are (1) to determine the significance of these glucose-transport modulations with respect to the anabolic responses in the thymocyte and (2) to determine what we can of the mechanism by which concanavalin-A and glucocorticoids alter transport activity. To determine the significance of glucose transport to anabolic regulation, we will vary these parameters by manipulating the medium glucose and test whether the functional relation between the two (glucose influx and macromolecular synthesis) is altered by modulating agents. A compartmental analysis of glucose transport will be carried out to find the extent to which transport at the plasma and nuclear membrane governs glycolysis within them. To determine the sequence of events leading to transport modulation, we will test for interference by drugs with reasonably defined target systems and by hormones. Cyclic nucleotides, Co ions fluxes and eventually other possible mediators of transport requlation will be measured under these conditions to find those which may be implicated in the modulatory mechanisms. Transport kinetic studies will be carried out in hopes of revealing the kind of interaction between the final regulator and the glucose carrier.