The time course of recovery of βadrenergic and VIP/helodermin receptors after homologous and heterologous down regulation was studied in the murine lymphoma cell line BL/VL3, a neoplastic equivalent of immature T cells. The heterologous part of isoproterenol down regulation was rapidly reversed, even in the presence of cycloheximide, suggesting that down regulation was linked to ligand-receptor interaction and/or cyclic AMP increase. Homologous down regulations of βadrenoceptors and VIP/helodermin receptors were less rapidly reversible and depended on protein synthesis as they were inhibited by cycloheximide: βadrenoceptors recovered faster than VIP/helodermin receptors.