From 1972 through 1982, 124 patients with muscle invasive T2/T3 bladder carcinoma without evidence of distant metastases were treated with definitive radiotherapy (60 Gy in 6 weeks) to the pelvis at The Norwegian Radium Hospital. Sections from paraffin embedded biopsies taken prior to the start of treatment were prepared for DNA flow cytometry, and 121 histograms were considered interpretable for DNA ploidy values. Significantly improved survival was seen in patients with the following characteristic, univariate analysis: T2 tumor, macroscopically complete removal of the tumor prior to radiotherapy, clinically complete response to radiotherapy, normal serum creatinine, absence of hydronephrosis, tetraploid tumor, WHO performance status 0 or 1, age below 65 years. In a multivariate analysis the following pretreatment variables turned out with prognostic power in this order: normal serum creatinine, T2 tumor, tetraploidy, and absence of small vessel invasion. When including response to therapy, the following factors were significantly predictive of a beneficial survival: clinically complete response after radiotherapy, normal creatinine, T2 tumor and tetraploidy. Tetraploidy was associated with response to radiotherapy when compared to diploid tumors (p = 0.07). This relationship alone did not explain the better survival of patients with tetraploid tumors, and other factors concerned with "tumor aggressivity" may be additional explanatory parameters. DNA ploidy values provide valuable information in the pretreatment situation concerning the prognosis for patients with T2/T3 bladder carcinoma.