Shortly after Morales' original report, several phase II trials confirmed the effectiveness of intravesical bacillus Calmette-Guérin (BCG) in superficial bladder cancer therapy. Concerns have been expressed about the toxicity related to this new therapeutic modality. These phase II trial data led European urologists to try to answer some questions related to BCG therapy, such as the optimal schedule and dose, the most effective BCG strain and the value of BCG compared with current chemotherapeutic drugs. To date, phase III trials have shown that BCG is more effective than thiotepa and doxorubicin in reducing tumour recurrences and progression and that BCG seems to be as effective as mitomycin C. Toxicity is significantly higher with BCG compared to chemotherapeutic drugs; no strain of BCG seems to be superior in this respect. Further studies are required to identify the optimal schedule and dose, as well as the best therapeutic efficacy/toxicity ratio.