The EORTC Urological Group is one of the 31 clinical groups and working parties within the European Organization for Research and Treatment of Cancer (EORTC). Intravesical chemotherapy has been used as chemoresection or chemoprophylaxis. Chemoresection has mainly been utilized in phase II studies to demonstrate ablation of existing disease and to study the mechanism of drug action. These studies are usually performed by individual members to obtain relevant information for the preparation of randomized trials. One example is a phase II chemoresection study with 4'-epi-doxorubicin (EPR). The EORTC GU Group extended its phase II trials to study remission in patients with primary carcinoma in situ. A new concept introduced in the prospective, randomized phase III trials includes the evaluation of chemoresection of a marker lesion as a prognostic factor in long-term prophylactic treatment. Chemoprophylaxis in the phase III trials aims to study the disease-free period, the recurrence rate and the long-term survival. So far, a series of five phase III trials, totaling more than 2,000 patients, demonstrated the efficacy of chemoprophylaxis to reduce tumor recurrence rates. The variation in the results of the different trials are due more to the prognostic factors (characteristics of the tumors) than to the related efficacy of the chemoprophylactic drugs. The selection of currently employed drugs, Mitomycin C, Epirubicin and BCG, is based on reported results, lack of toxicity, and drug availability in Europe. The data collected will be of great importance to determine the optimal clinical management of superficial bladder cancer.