A prospective randomized controlled study on the effect of KLH (keyhole limpet hemocyanin) versus etoglucid in the prevention of recurrences in primary and recurrent superficial transitional cell carcinoma of the bladder (stage pTa-pT1, grades 1-3 according to the recommendations of UICC and WHO) after complete transurethral resection of the tumor started in 198. Patients in group 1 (n = 76) were immunized with 1 mg KLH intracutaneously, after which they received bladder instillations of 30 mg (30 ml) KLH weekly for 6 weeks and then monthly for 1 year. Patients in group 2 (n = 85) received weekly bladder instillations of 0.565 g etoglucid (50 ml 1% solution) for 6 weeks and then monthly for 1 year. The percentage of recurrences, recurrence rate, disease-free interval and tumor progression rate were evaluated for both treatment groups. The end-point of the study was progression in stage or grade or more than two recurrences during the observation period. The shortest follow-up was 12 months, the mean follow-up, 27.5 months. No statistically significant differences were found between the two groups in percentage of recurrences (43.4% KLH-53.9% etoglucid), recurrence rate (4.4 KLH-3.9 etoglucid), mean disease-free interval (12.1 months KLH-13.6 months etoglucid) or progression rate (6.5% KLH-9.4% etoglucid).