In a prospective randomised controlled study, the efficacy of ethoglucid was compared with that of keyhole-limpet haemocyanin (KLH) in preventing recurrent tumours following transurethral resection of primary superficial transitional cell carcinoma of the bladder. Patients treated with ethoglucid (n = 39) received 0.565 g (1% solution) ethoglucid weekly for 6 weeks and then monthly for 1 year. Patients treated with KLH (n = 38) were immunised subcutaneously with 1 mg KLH; bladder instillations of 30 mg were then given weekly for 6 weeks and thereafter monthly for 1 year. The recurrence rates, disease-free intervals and tumour progression rates were evaluated. The end-point of the study was either progression in stage or grade or more than 1 recurrence during the observation period. The minimum length of follow-up was 1 year. The recurrence rates, mean disease-free intervals and progression rates in the 2 groups showed no statistically significant differences.