Pardaxin is an antimicrobial peptide of 33 amino acids, originally isolated from marine fish. We previously demonstrated that pardaxin has anti-tumor activity against murine fibrosarcoma, both in vitro and in vivo. In this study, we examined the anti-tumor activity, toxicity profile, and maximally-tolerated dose of pardaxin treatment in dogs with different types of refractory tumor. Local injection of pardaxin resulted in a significant reduction of perianal gland adenoma growth between 28 and 38 days post-treatment. Surgical resection of canine histiocytomas revealed large areas of ulceration, suggesting that pardaxin acts like a lytic peptide. Pardaxin treatment was not associated with significant variations in blood biochemical parameters or secretion of immune-related proteins. Our findings indicate that pardaxin has strong therapeutic potential for treating perianal gland adenomas in dogs. These data justify the veterinary application of pardaxin, and also provide invaluable information for veterinary medicine and future human clinical trials.