In a prospective multicenter study, four protocols for administration of mitomycin C and Adriamycin by intravesical installation were evaluated for effectiveness in the prevention of recurrent tumours in patients whose superficial bladder tumours (TA and T1) had been removed by transurethral resection. The 3-year and short-term installation protocols were compared with each other and each with a combination of the two. Evaluation after a mean follow up of 62.5 months was possible in 333 patients: the overall recurrence rate was 20.7% and the overall progression rate, 9.3%. No statistically significant differences were found in frequency of tumour recurrence among three mitomycin regimens and an Adriamycin regimen, regardless of the risk groups. However, frequency of recurrence per time unit was much lower in the treatment group with short-term intensive (weekly) mitomycin instillation, which was due mainly to prevention of late recurrence.