The proliferation rate as determined by Proliferating Cell Nuclear Antigen (PCNA) immunostaining and the DNA ploidy status as measured by static cytometry were studied in 70 transitional cell carcinomas of the bladder (TCCB) in relation to grade, stage, and recurrence. The follow-up period was 2 years. A significant difference was observed in PCNA expression among grades I, II, and III (P < 0.02), between superficial (pTa-pT1) and invasive (pT2-pT4) tumors (p < 0. 04), between recurring and non-recurring tumors (p < 0.001), and between tumors of the same grade with and without recurrence (p < 0. 05). A significant difference was also found in the ploidy pattern among grades I, II, and III (p = 0.002), and between superficial and invasive (p = 0.02) and recurring and non-recurring tumors (p < 0. 01). Finally, the recurrence status seems to be strongly influenced by the proliferation rate and ploidy of TCCB (p < 0.001). Our results suggest that the above-studied parameters may offer useful information on the biological behavior of TCCB.