In 12 patients of the dental department of the surgical clinic of the University of Veterinary Medicine Vienna, the efficacy of a new, long-acting, single subcutaneous injection of a third generation cephalosporin (Convenia (R)) was evaluated. On day zero, when the subcutaneous injection was administered, gingivitis index and the amount of plaque was assessed as well as 10 days later, immediately before plaque and calculus were removed. The exact amount of plaque was determined in pixels by means of digital photography with standardized scale and computer-aided planimetry. Gingivitis index was reduced after subcutaneous injection from initially 0, 18 + /- 0,014 to 0,04 + /- 0,007 (p < 0,0005) within 10 days without any additional treatment (reduction of 78%). Plaque areas were reduced from initially 9124,49 pixels to 3495,59 pixels (p < 0,0005) within 10 days without any additional treatment (reduction of 62 %). Prolonged-acting Cefovecin (Convenia (R)) is a beneficial contribution before, during and after treatment of periodontal patients as well as a benefit to veterinarians.