Fragile sites expression induced by 25 μg/ml and 50μg/ml bromodeoxyuridine (BrdU) were studied in lymphocyte culture of 15 healthy Egyptian water buffalo (9 females and 6 males). In each animal, 100 metaphases were examined, the cells were scored for chromosome number and types of structural abnormalities. A site showing a gap or break was defined as fragile and reexamined after G-banding to identify the fragile site involved. The results showed significant difference (p<0.01) between 2 different doses of BrdU in the total aberrant cells and total structural abnormalities [20.5±3.9%, 42.6±3.5% (25μg/ml BrdU) and 26.9±6.4%, 55.9±10.9% (50 μg/ml BrdU), respectively]. A significant decrease in mitotic index in the treated culture was observed in respect to control culture. The difference between females and males was found to be significant in the total aberrant cells and total structural abnormalities in dose 50 μg/ml BrdU [44.2±3.2%, 40.2±2.4% and 63.3±5.6%, 44.7±5.8%, respectively]. Our results indicated that the common fragile sites are chromosome bands 2p13, 2q21, and 5q21. This is the first report of BrdU-inducible fragile sites in the genome of buffalo.