Here, we report that BCG induces a rapid intracellular Ca2+ (calcium ion) signal in bladder cancer cells that is essential for activating the transcription factor nuclear factor kappa‐light‐chain‐enhancer of activated B cells (NF‐κB) and for synthesizing and secreting proinflammatory cytokines, including interleukin 8 (IL‐8). The gene discussed is NFKB1; the disease is urinary bladder carcinoma.