The progeny of cows infected with Brucella abortus could acquire the bacterium during their fetal stage and generate immune tolerance. In order to identify them, a clinical assay was conducted with two groups of seronegative calves. In Group I, seven bovine females received a standard S19 dose, and in Group II, eight males served as control. All animals were sampled seven times by official serological tests every 45 days. Also, complete blood with anticoagulant was collected and tested by the polymerase chain reaction (PCR) 45 and 135 days after vaccination. Results were analyzed by the test of proportions. In Group I, all the animals had their maximum antibodies title at the first sampling, but from the fourth sampling, their titles decreased until they became undetectable for the screening test. All animals in Group II remained negatives. Animals from both groups recorded negative with PCR. Significant differences (P<0.05) between groups were observed for seroconversion in the first two samplings. It was concluded that none of the tested animals were immunotolerant and that PCR may not be an appropriate method to demonstrate immunotolerence in some individuals.