Recent advances in hybridoma technology have allowed the development of homogeneous immunologic reagents of defined specificity, activity, and reproducibility. During the last few years, the number of monoclonal antibodies directed against bacteria has increased exponentially, and research investigations have focused on the use of monoclonal antibodies for the diagnosis and therapy of infectious diseases. Monoclonal antibody technology offers a rapid, specific diagnosis of bacterial infection, long before culture results are available. We have described the use of monoclonal antibodies for the detection of group B streptococcal (GBS) infections in mothers and infants at risk to develop invasive GBS disease. Specifically, we have used the anti-GBS monoclonal antibodies to detect GBS colonization, serotype bacterial isolates in the laboratory, and identify GBS antigens in body fluid specimens. We have also discussed the use of anti-GBS monoclonal antibodies to confer protection against fatal infection in mice. Monoclonal antibodies against group A streptococcus and Streptococcus pneumoniae have also been developed with the potential for the rapid diagnosis of serious and often life-threatening infections, particularly in immunocompromised individuals. With further refinements in monoclonal antibody technology in the future, streptococcal hybridomas may replace standard culture techniques for bacterial identification in the microbiology laboratory.