Seventy-five patients with recurrent bladder carcinoma were randomized after electroresection to receive either epirubicin (E) or epirubicin + verapamil (E + V) instillation of the bladder at regular intervals for 2 years. Samples of the bladder wall, tumour tissue and peripheral blood were taken from 20 patients. The average follow-up period was 21 months. Fifty per cent of the patients in the E group and 37% in the E + V group developed recurrent tumours. Recurrence rates (RR) were 6.3 and 4.7, respectively. Before the instillation therapy the RR was 16.0. There was a highly significant reduction of RR during the instillation therapies; in group E p less than 0.005 and in group E + V p less than 0.001. The difference between the treatment groups was not statistically significant. Verapamil increased epirubicin concentrations in both the bladder wall and the tumour tissue, but did not affect concentrations in the peripheral blood. Side effects were few and did not lead to discontinuation of treatment.