Eleven patients with advanced bladder cancers (T2-4) were treated by intra-arterial CDDP infusion therapy and intratumoral Pt concentrations were measured. The following results and suggestions were obtained by comparing the histological effects and intratumoral Pt conc. 1) By calculating cross section areas from diameter of blood vessels, the blood flow distributions of tumor feeding arteries were estimated. Based on this distributions, the distributed CDDP dosage flowed into the tumor feeding arteries was calculated. The distributed CDDP dosage of histologically effective group (N = 5, Grade IIb less than by Shimosato histological evaluation) were significantly higher than that of ineffective group (N = 6, Grade IIa greater than). (p less than 0.02, Student t test). 2) A good correlation was obtained between the revised intratumoral Pt value by distributed CDDP dosages and intervals from intra-arterial infusion therapies to operations. (r = -0.90, p less than 0.001). Intratumoral Pt conc. declined with a half life of 12 weeks. 3) Based on the declined linear line calculated from 2), theoretical intratumoral Pt conc. which was presumed value on day 0 (just after intra-arterial infusion therapy) were calculated. Theoretical Pt conc. of effective group were significantly higher than that of ineffective group (p less than 0.01), although no significant difference was seen between two groups compared by net intratumoral Pt conc. 4) A good correlation was seen between theoretical intratumoral Pt conc. and distributed CDDP dosage (r = 0.89, p less than 0.01). 5) Five of 6 cases with above 5 micrograms/g of theoretical intratumoral Pt conc. were histologically effective, and 5 micrograms/g of theoretical Pt conc. corresponded to 31 mg of distributed CDDP dosage.(ABSTRACT TRUNCATED AT 250 WORDS)