Purpose: To evaluate the effect of surgical placement of an aminoguanidine (AG)-loaded chitosan membrane, which allows slow local release of AG, over an endosseous implant on mechanical retention of the implant in nondiabetic and diabetic rats. Materials and Methods: Forty-eight male Wistar rats were randomly divided into six groups of eight animals each and subjected to three different treatment modalities: (1) implant placement in the femur, (2) placement of implant + chitosan membrane without AG at the surgical site, or (3) placement of implant + AG-loaded chitosan membrane (AG concentration of 7.35 mmol/kg body weight) at the surgical site. Groups 1, 2, and 3 were nondiabetic (control groups), and groups 4, 5, and 6 had chemically induced type 1 diabetes (test groups). At 4 weeks after implant placement, the animals were sacrificed and the countertorque force (CTF) required to disrupt the bone-implant interface was measured. Analyses of variance were performed, and the mean CTF values were compared between groups by using the Student t test. Results: The mean CTF values were significantly lower in diabetic groups not treated with AG than in the corresponding nondiabetic animals that had received the same treatment modality. In groups that received AG locally, the mean CTF values were not statistically significantly different, regardless of diabetes status. Conclusions: Induced diabetes (type 1) negatively affected the CTF necessary for disrupting the bone-implant interface. Local availability of AG in diabetic animals led to an increase in the CTF values to the same level as that in nondiabetic animals.