BACKGROUND:Cystitis and pyelonephnitis in ruminants mostoften result from ascending urinary tract infection (UTI).OBJECTIVES: Investigating the prevalence of urine infection andits relationship with histopathological findings of bladder andkidney. METHODS: This study was carried out on 353 slaughteredbuffalos (143 female and 210 male) at Ahvaz abattoir, southwest ofIran. After slaughter, urinary samples were taken directly frombladder by sterile syringe. The bladder and kidney were inspectedand samples from them were taken for histophatological study. Allof the urine samples were incubated for isolation of bacteria onblood agar and MacConkey. Biochemical characterizations of theisolates were performed according to Bergey's manual of systemicbacteriology. Histopathological samples were taken fromrepresentative parts of each bladder and kidney and were stainedwith haematoxylin and eosin. RESULTS: Out of the 353 urinesamples, 19 (5.38%) were positive. The percentages of infectedcattle in female and male were 6.3% and 4.8%, respectively. Thesebacteria were isolated: E.coli (21%), Staphylococcus spp. (31.6%),Streptococcus spp. (15.8%), Proteus spp. (15.8%), Klebciella spp.(5.3%), Yercinia spp. (5.3%), and Actinimyces and Pasteurelle spp.(5.3%). In histopathological examination, 51(14.4%) and 5 (1.4%)of the buffalos had chronic cystitis and pyelonephritis, respectively.Bacteria were isolated only in 3 cases of chronic cystitis and 2 casesof pyelonephritis. Statistical analysis showed there was norelationship between isolation of bacteria from urine with cystitisand pyelonephritis. CONCLUSIONS:Some cases of chronic cystitisare not able to isolate of bacteria from urine and for causingpyelonephritis they need predisposing factors which caused urineretention.