Following pretreatment with clindamycin, cleaning, scaling, polishing, and curettage, six beagles that were patients at the Dental Department of the Clinic for Surgery and Ophthalmology of the University of Veterinary Medicine of Vienna received a doxycycline polymer filling (Doxirobe, Pharmacia Animal Health) in periodontal pockets of teeth 204, 208, 304, and 309. Gingivitis index, gingival crevicular fluid, probing depth, and attachment loss were determined before and 6 and 12 weeks after treatment. Teeth 104, 108, 404, and 409 did not receive antibiotic therapy but were pretreated in the same manner as the doxycycline-treated teeth. Pocket depth for teeth treated with doxycycline was significantly reduced (improved) by 39% after 6 weeks (P =.001) and by 35% after 12 weeks (P =.001). Pockets around control teeth were improved after cleaning and curettage but were still significantly deeper than around teeth treated with doxycycline. Compared with control teeth, teeth treated with doxycycline had significantly less gingival crevicular fluid after treatment (P =.001). Teeth treated with doxycycline gained significant attachment after 6 (42%) and 12 (38%) weeks. Significantly fewer bacteria were harvested from doxycycline-treated teeth than from control teeth. The gingival index was significantly lower in the doxycycline-treated teeth than in the control teeth 6 (P =.002) and 12 (P =.007) weeks after treatment. Local application of doxycycline complements traditional subgingival curettage therapy in a reasonable and effective way and can significantly improve treatment success, especially with regard to pocket depth reduction and attachment gain.