Treatment of Catharanthus roseus hairy roots with antagonists, like verapamil and CdCl2, that block the Ca2+ flux across the plasma membrane enhanced the total alkaloid content by 25% and their secretion 10 times. The specific Ca2+ chelator, EGTA, stimulated 90% of the total alkaloid secretion. Treatment with inhibitors of intracellular Ca2+ movement, like TMB-8 and trapsigargin, enhanced the total alkaloid content by 74% and their secretion into the culture media by 4- to 6-fold. The results suggest that an inhibition of external and internal Ca2+ fluxes induces an increase in the indole alkaloid accumulation and secretion in C. roseus hairy roots.