Positive serological tests for brucellosis (positive rose bengal plate agglutination test ans/or positive complement fixation test) were found in the cattle of previously uncontaminated or long ago decontaminated areas of the department of the Puy-de-Dome (France). In the 1992-1993 prophylaxis campaign, 1 0 % of the sera of the bovine livestock in some of these areas were positive. Epidemiological studies demonstrated that most positive sera were not related to brucellosis clinical cases, suggesting the recent occurence in the Auvergne of an epidemic due to a new bacterial agent cross reacting with brucella serology.