Thirty three patients with carcinoma in situ (CIS) or/and numerous recurrences of superficial bladder tumor were treated with intravesical BCG after transurethral resection. 63% of patients with CIS were free of recurrence after two years, two underwent cystectomy and one died because of progression. Patients with Ta and concomitant CIS responded well to BCG, while the patient with T1 tumor and CIS was free from recurrence for 15 months. Dysplasia of grade II disappeared after BCG. 62% of patients with Ta tumor were without recurrence after one year, but after two years 86% of the patients had recurrences. Patients with T1 tumor were free from recurrence for eight months, after which 25% had progression. The side effects of BCG were transient: urinary frequency in 48%, malaise in 39%, dysuria in 36%, haematuria, bladder pain and fever in 24%. 15% of the patients required isoniazid treatment. It is concluded that intravesical BCG is beneficial in CIS and superficial bladder tumors.