The work presents results of investigations on Q fever seroepizootology in Bulgaria during the last five years. These data are compared with the preceding period from 1950 to 1983. The basic method for investigation is Complement fixation test. Also used are immunofluorescence, agglutination reaction, cultivation and direct Electron microscopy. In general 15,814 samples were tested. Q fever positivity was foundin 10.08% of cattle, 20.44% of sheep, 10.17% of goats, 59.25% of dogs, 26.66% of magpies, 11.11% of wood-pigeons, 7.40% of mouflons, 7.14% of foxes and 5.82% of hens. These data confirm the results of our preceding investigations for the wide dissemination of C. burnetti among domestic animals. Positive data for the significant spread of C. burnetti among the wild animals and birds also exists. The disease manifests itself clinically in abortions in sheep and cattle and mastitis in sheep. The inapparent form, however, is much more frequent. The infected dogs represent a special interest. The control measures are based on the wide use of tetracyclines. The presented data testify to the continuing importance of the problem of Q fever in Bulgaria.