The primary aim of the study was to test the influences of thapsigargicin in releasing Ca2+ from the intracellular Ca2+ stores and comparing it with the effects of thapsigargin. In this study, the effect of tumour promoter thapsigargicin on intracellular Ca2+ has been described. Therefore, rat liver endoplasmic reticulum subcellular fractions (microsomes) were employed and Ca2+ movements measured by spectrofluorimeter. Fluo-3 studies were used to follow Ca2+ release in experiments with microsomes. When results are evaluated, it has been concluded that like thapsigargin, thapsigargicin has the ability of discharging the intracellular Ca2+ stores, increasing the intracellular free Ca2+ concentration ([Ca2+]i) and being a potent and specific inhibitor of the ER Ca2+-ATPase.