BACKGROUND: The epiphyseal growth plate is an important anatomical segment localized on the ends of a long bone. Despite the abovementioned atractive reasons for alendronate's use, few data on the effect of alendronate during epiphyseal growth exist. AIM: Verify the effect of alendronate on the growth epiphyseal plate, and compare its effect with the size of the femur during the double-staining of the immunolocalization of transforming growth factor-ß1 (TGF-ß1) and bone morphogenetic protein-2 (BMP2) in endochondral ossifing in specimens that have received alendronate. METHODS: Forty newborn rats were randomly divided into two groups: a control group (were given applications of 1 mg/kg physiologic saline) and a group that received Alendronate (a dose of 2.5 mg/kg). These groups were then divided into two subgroups for euthanasia in two and 12 d of life. After euthanasia, the femurs were removed, and the femoral bones were measured linearly between the apex of the greater trochanter until the lower intercondylar midlle face to verify the probable bone growth between 3 and 12 d in control and alednroanto treated rats. Posteriorly, the surgical pieces were also sent to the histopathology laboratory to produce histological slides. The obtained slides were stained with hematoxylin and eosin to measure each of the cartilage zones in endochondral development. and other slides were immunohistochemically tested for anti- TGF-ß1 and BMP-2 antibodies to investigate the immunolocalization of these proteins in the epiphyseal plaque area. RESULTS: On the third day, some diferences between the control group and specimens treated with alendronate were verified. Macroscopiccaly, we found similarities in size between the femoral bones when we compared the control group with the specimens that received alendronate. On the 12th day, the bone size of the mice receiving the drug was significantly smaller than those of the control group. These results coincide with changes in the TGF-ß1 and BMP-2 expression. In the specimens that received alendronate, the TGF-ß1 was expressed in some sites of trabecular bone that was neoformed, peripherally to the bone marrow area. The BMP-2 was also positive in proliferative chondrocytes and hypertrofic chondrocytes. On the 12th day, all layers of chondrocytes exhibited positivity for BMP-2 in the specimens that received alendronate. In the interface between the trabecular bone and cartilage, an area of disorganized bone deposition was evident. Neoformed bone also appeared to be different at 12 d. In the control group, BMP-2 was positive in an intense area of bone trabeculae, whereas the alendronate-treated group showed TGF-ß1 positive trabeculae and a greater bone area. CONCLUSION: Alendronate alters the immunolocalization of TGF-ß1 and BMP-2 simultaneously, a condition that changes the usual histological aspects of the cartilage zone and impairs epiphysis growth and femur growth.