To elucidate the role of calcium release from internal stores during different paradigms of tetanisation in long-term potentiation (LTP), we have investigated the effects of thapsigargin on the elevation of the excitatory postsynaptic field potential (fEPSP) and the population spike (PS) after tetanisation. We found no effect on the duration of fEPSP potentiation if thapsigargin was perfused before strong (triple) tetanisation. However, the potentiation was reduced significantly from control experiments if thapsigargin was applied before weak (single) tetanisation. Surprisingly, we did not find any reduction of PS potentiation, which could be due to changes in the recurrent inhibition. We conclude that the involvement of internal calcium release in the mechanisms of LTP induction will be reduced if multiple tetanisation is used.