In the thymus, sympathetic nerves run in septa in close connection to subcapsular/perivascular thymic epithelial cells (TEC). Since TEC are supposed to create a microenvironment of cytokines necessary for the development of thymocytes to T cells, we investigated the influence of sympathetic transmitters and co-transmitters on interleukin-6 (IL-6) synthesis in cultivated rat TEC that express markers of perivascular/subcapsular TEC. Noradrenaline and ATP stimulated IL-6 production in the culture supernatants 14- and 23-fold over basal values after 24 h. Co-stimulation with noradrenaline and ATP yielded an additive effect. Synthesis of IL-6 was concentration-dependent upon ATP and appeared to be mediated by P<sub>2</sub> purinoceptors. During 24 h stimulation with 1 mM ATP, two thirds of the ligand was degraded mainly to ADP, production of AMP and adenosine was minor or negligible. Thus, in TEC, transmitters and co-transmitters of the sympathetic nervous system have a co-stimulatory effect on synthesis of IL-6 that is an important factor for thymocyte differentiation and proliferation.