Abstract:The pharmacological activity of dipyridamole has been related to its ability to increase intracellular cAMP. Elevated cAMP concentrations can tone down T‐cell effector functions. The aim of this study was to evaluate the dipyridamole effectin vitroon the generation of alloreactive cytotoxic and lymphokine‐activated killer cells in normal T‐cell subpopulations. Dipyridamole suppressed T‐cell cytotoxic functions in a dose‐dependent way. The kinetics of suppression showed that dipyridamole prevented the first step of cytotoxicity, i.e. activation of the lytic program following allogeneic or interleukin‐2 stimulation. The ability of dipyridamole to interact with the immunosuppressive activity of cyclosporine was also investigated. By itself, cyclosporine suppressed the generation of alloreactive cytotoxicity, but not the generation of lymphokine‐activated killer cells. A synergistic immunosuppressive activity between dipyridamole and cyclosporine was observed on the generation of alloreactive cytotoxic