Analgesia of the wide surgical excision region in surgeries such as bilateral radical mastectomy plays an important role in postoperative care. Opioids are effective in alleviating pain; however, they are sometimes difficult to obtain in most local veterinary hospitals. The objective of this research was to compare the efficacies of (1) onsite infiltration analgesia with lidocaine and bupivacaine (group I, [Formula: see text]) and intravenous injection with buprenorphine and (2) constant rate infusions (CRIs) of fentanyl and ketamine (group II, [Formula: see text]) for postoperative analgesia after bilateral radical mastectomy and ovariohysterectomy in dogs with mammary tumors. The results showed that a combination of infiltration with lidocaine and bupivacaine and intravenous injection with buprenorphine was as effective as CRIs of fentanyl and ketamine. Infiltration analgesia with lidocaine and bupivacaine may be an option for analgesia in dogs undergoing bilateral mastectomy and ovariohysterectomy and may help reducing pure [Formula: see text]-opioid requirements.