BACKGROUND: Bladder carcinoma is the most common malignancy of the urinary tract. Approximately 75-85% of patients present non-muscle invasive bladder cancer (NMIBC). Standard primary treatment for NIMBC is transurethral resection (TUR) followed by intravesical Bacillus Calmette-Guerin (BCG) immunotherapy. BCG has been accepted as the most effective agent in clinical use against NMIBC. Various BCG substrains are used worldwide for bladder cancer immunotherapy although the impact of used BCG substrain on BCG antitumor capacity is a little investigated. OBJECTIVES: The aim of this study was to compare the antitumor capacity and the ability to trigger cytokines production of three BCG substrains by stimulation of the local innate immunity in vitro. MATERIAL AND METHODS: The human bladder cancer cell line T24 was co-cultured with each of the BCG substrains: Moreau, Tice and RIVM alone or with BCG pretreated DCs (dendric cells) and allogenic PBMCs derived from the same donor. The inhibition of T24 cell growth was evaluated by 3H-thymidine incorporation. Production of Th1 cytokines (IFN-γ, TNF-α, IL-12) and Th2 cytokines (IL-10, IL-4) was measured in cultures of BCG-activated PBMCs by ELISA test. RESULTS: An approximately two-fold inhibition of T24 cell proliferation was observed as a direct cytotoxic effect of tested BCG substrains on T24 cells. However, BCG inhibited the growth of tumor cells mainly by activating the effector cells of innate immunity. About a 10-fold inhibition of T24 cell proliferation was observed when T24 cells were co-cultured with allogenic BCG pretreated DCs and PBMCs derived from the same donor. The PBMCs activated by compared live BCG substrains secreted large amounts of TNF-α and IFN-γ cytokines. CONCLUSIONS: Tested BCG substrains had little direct inhibitory effect on T24 cell proliferation. Moreau evolutionarily early BCG substrain showed similar strong, indirect antitumor effects as evolutionarily late BCG substrains Tice and RIVM.