The therapeutical efficiency of three (day 0, 2 and 4) deep subcutaneous injections behind the angular process of the mandible of I ml of an immunemodulator (Zylexis((R))) in 17 cats with chronic gingivostomatitis which derived from multi-cat households was assessed by plaque- and gingivitisindex, by evaluation of the inflammation of the mucosa via comparing to the PANTONE (TM) color sheets and by computer-aided colorimetric luminance measurement. The initial baseline plaque-index (4 grades) of 2.38+/-1.13 decreased to 1.57+/-1.08 (p < 0.001) after 10 days, the initial baseline gingivitis-index (4 grades) of 2.49+/-1.14 decreased to 1.30+/-1.10 (p < 0.001) after 10 days. Due to the reduced redness, the baseline colour value increased from 57.00+/-38.44 to 124.73+/-27.17 (p < 0.001) after 10 days and the baseline computer-aided luminance value increased from 96.18+/-23.47 to 122.76+/-22.67 (p < 0.001) after 10 days due to decreased inflammation of the gingiva and oral mucosa. Calicivirus, isolated from oral swabs could be detected in 15 out of 17 cats. In none of these swabs feline herpes virus (FHV-1) was detected. The influence of the treatment with the immunemodulator on Calicivirus-specific T-lymphocytes was analysed in blood of 4 of the 15 cats positive for Calicivirus. However, repeated injections of Zylexis((R)) did enhance only in one animal the Calicivirus-antigen-specific in vitro T-cell reactivity. Thorough questioning of the owners revealed in all patients a marked improvement in well-being and an ameliorated food uptake. All owners reported, that their pets showed obviously less pain during food uptake. Many owners reported, that just few days after the first subcutaneous injection the hair coat was more shiny, the hair loss decreased and the cats showed a more friendly and trusting behaviour. Therefore the immunemodulator Zylexis((R)) is a safe and recommendable supplement to the already known possibilities of the treatment of chronic gingivostomatitis in cats.