Integral photodynamic therapy with hematoporphyrin derivative was performed on 35 patients who had resistant transitional cell carcinoma of the bladder, mainly carcinoma in situ. The light source was an argon ion pumped dye laser (wavelength 630 nm.) using rhodamine B. Two types of laser light scattering diffuser developed at our department were used: a motor driven laser light scattering diffuser with computer regulation, and an endoscope modified light scattering diffuser tipped with a small quartz bulb containing a lipid nutritious solution as the scattering medium. The total energy density used was 10 to 30 J./cm.2. Of the 35 patients 24 (68.6%) achieved a complete response and 5 (14.3%) a partial response at 3 months. In 10 of the 24 patients there was no recurrence with an average tumor-free interval of 20.9 +/- 16.7 months, ranging from 5 to 60 months. Bladder capacity was decreased to approximately 150 ml. for 3 months after the integral photodynamic therapy without any evidence of hydronephrosis on excretory urograms, except for 2 patients who had a contracted bladder before photodynamic therapy. Integral photodynamic therapy may prove to be useful for the treatment of carcinoma in situ of the bladder.