The therapeutical efficiency of a subgingival injection of 1,25 ME of feline recombinant interferon omega per jaw quadrant in 20 cats with severe chronic gingivostomatitis was assessed by indices (plaque, gingivitis), by evaluation of the redness of the mucosa via comparing to the PANTONE(TM) color sheets and via computer-aided colorimetric luminance measurement. The initial baseline plaque-index (4 grades) of 2,21 +/- 1,33 decreased to 1,84 +/- 1,27 (p<0,001) after 10 days, the initial baseline gingivitis-index (4 grades) of 2,15 +/- 1,12 decreased to 1,62 +/ 1,04 (p<0,001) after 10 days, the baseline colour value increased due to the reduced redness from 57,63 +/- 31,39 to 95,77 +/ - 34,68 (p<0,001) after 10 days and the baseline computer-aided luminance value increased from 94,44 +/- 19,55 to 119,87 +/- 23,65 (p<0,001) after 10 days due to decreased redness of the gingiva and oral mucosa. Calicivirus, harvested from oral swabs could be detected in 9 out of 10 cats from multicat-households. In one of these swabs additionally FHV-1 could be detected. No FeLV, FIV or FCV could be detected in therapeutically justified specimens from gingiva or oral mucosa. Thorough questioning of the owners revealed in all 20 patients a marked improvement in wellbeing and an ameliorated food uptake in 18 patients. Only few days after the subgingival injection, most owners recognized that their pet had less obvious pain, was more friendly and trusting, did not hide away, gained a better and more shiny hair coat and ate more and better. The subgingival injection of Virbagen(R) Omega is a valuable supplement to the presently known arsenal for treatment of chronic oral diseases and is especially recommended as an additional tool to professional dental and periodontal treatment. Besides a significant reduction of pain due to decreased inflammation of the gingiva and oral mucosa and the significantly lower plaque index as a marker for lower amount of bacteria, the obvious change in behaviour reported by the owners was the most prominent result.