The　dynamics　of　the　generation　of　the　various　spike　trains　in　neural　pacemakers　is　of　fundamental　importance　to　the　understanding　of　neural　coding.　Recent　studies　have　demonstrated,　theoretically　and　experimentally,　that　neural　pacemakers　produce　chaotic　oscillations.　Deeper　analyses　in　several　neuronal　models　have　revealed　many　nonlinear　phenomena　including　period-adding　bifurcations　whose　existence　has　not　been　experimentally　confirmed.　Zn　this　letter,　we　reported　that　the　period-adding　bifurcation　with　chaos　was　observed　in　the　interspike　interval　(ISI)　series　generated　by　an　experimental　neural　pacemaker　when　the　extracellular　calcium　concentration　was　changed　or　a　potassium　channel　blocker　was　administered　at　the　site　of　the　pacemaker.　We　also　simulated　our　experimental　discoveries　by　computing　a　generalized　model　of　excitable　cells.　The　chaotic　phenomenon　in　the　experiment　and　that　in　the　model　were　demonstrated　and　compared　using　the　nonlinear　forecasting　and　surrogate　data　methods.