In this preliminary report, we describe our inability to induce IgE antibody to a well-characterized bacterial component, the membrane proteoglycan of Klebsiella pneumoniae and its major protein fraction FIII-B in BALB/c mice. In contrast, an immunomodulatory effect of membrane proteoglycan of K. pneumoniae on the IgE and IgG antibody responses to ovalbumin could be demonstrated.