A serological and bacteriological study was performed with sera taken from 2,228 swine from six states in Venezuela. None of the animals were vaccinated against brucellosis, and the prevalence of the disease varied from 5 to 89% on farms located in these states. Our studies indicated that the animals could be categorized into four groups depending on the degree of reactivity in serological tests. Brucella suis biovar 1 was isolated from the lymph nodes, spleens, and semen samples of seropositive animals and identified by oxidative metabolic techniques. B. suis could not be isolated from tissues of seronegative swine even from farms with cases of the disease (detected by serology). Results suggest that, although the immunodiffusion assay using Brucella melitensis B115 polysaccharide B or B. abortus 1119-3 O-polysaccharide could be useful in the detection of active infections, it is perhaps not as sensitive as some of the other standard serological tests used in this study for the detection of swine brucellosis.