Fifty-three patients with carcinoma in situ of the bladder were treated with Evans strain BCG given intravesically. Complete remission was achieved after either one or two 6-weekly courses in 53% of patients. The median duration of remission was 32 months. Treatment-related bladder symptoms were minor during the first course, more severe during the second. There was no relation between severity of symptoms and likelihood of response. With a median follow-up of 32 months, disease progression has occurred in 10% of complete responders, whereas failure to respond on either cystoscopic, histological or cytological grounds was associated with a 48% progression rate. Although intravesical BCG produces impressive responses in carcinoma in situ of the bladder, managed conservatively the condition remains a dangerous one.