Serum samples collected from feral swine (Sus scrofa) throughout Florida (USA) from 1974 to 1989 were tested for antibodies to Brucella sp. by the card test, the standard tube test, the rivanol test or the complement fixation test. Seropositive swine were detected at six of 18 sites with a composite prevalence of 23.4% (238 of 1,015 samples; range = 5.5% to 33.3%) for sites with seropositive swine. At one site for which age and sex data were available there was no significant difference (P = 0.50) in seroprevalence between males and females. Antibody prevalence in adult (> or = 8 mo) and juvenile swine (< 8 mo), however, was significantly different (P < 0.05). Based on these data, Brucella sp. infections are limited only to certain populations of feral swine. To avoid the spread of Brucella sp. organisms, however, relocation of feral swine is not recommended.