24 patients with muscle invasive carcinoma of the bladder were treated in a pilot study of twice daily fractionation at radiation doses of 1.8-2.0 Gy per fraction to total doses of 54-64 Gy to the bladder and 39.6-44 Gy to the whole pelvis. The treatment aim was to give 32 fractions in 22 days. The interfraction interval was a minimum of 6 h. The principle objective was to record acute and late tolerance, but local control and survival data is also presented. Acute radiation morbidity was scored according to the RTOG system. Grade 2 large bowel effects were seen in 52% of patients, Grade 3 effects in 26% and there was one Grade 4 and one Grade 5 effect. The mean duration of effect was 4.5 weeks although the more severe reactions were also more protracted. Grade 2 urinary effects occurred in 30% and Grade 3 in 17% of patients. The mean duration of effect was 7.2 weeks. There were no Grade 4 or 5 acute urinary effects. Late radiation morbidity was scored according to the EORTC/RTOG system and was assessable in 16 cases who survived more than 6 months. There were two cases (12%) of Grade 1 bowel toxicity, two cases of Grade 1 and three of Grade 2 urinary toxicity. There were no cases of late skin effects. Actuarial analysis at 2 years shows a local control probability of 56% and survival probability of 35%.