Enzyme-linked immunosorbent assays were conducted on milk of cows from which Brucella abortus was isolated and that of noninfected controls. Horseradish peroxidase-labeled rabbit antibovine immunoglobulins IgG, IgG1, and IgA were used as conjugates. A heat-killed whole-cell suspension of B abortus strain 19 was used as the antigen. Differences in antibody profiles were observed in milk of cows from which B abortus was isolated and in milk of noninfected cows. Antibody profiles were similar in milk of cows infected with B abortus and that of cows from which B abortus strain 19 was isolated.