Patients who undergo splenectomy are at greatly increased risk for overwhelming pneumococcal bacteremia and death. Twenty-three-valent pneumococcal polysaccharide vaccine (PPV-23), which contains capsular polysaccharides (PSs) from 23 common serotypes of Streptococcus pneumonias, is strongly recommended for such patients. The capacity to respond to PPV-23 by producing immunoglobulin (Ig) G is genetically regulated. Some proportion of adults do not respond and, despite postsplenectomy administration of PPV-23, may remain susceptible to recurrent pneumococcal sepsis. Here, we describe 2 patients who had recurring pneumococcal bacteremia after undergoing splenectomy despite having received numerous doses of PPV-23. Heptavalent protein-conjugate pneumococcal vaccine (PCPV-7) was then administered, and it induced high levels of IgG to all 7 PSs; in one of the patients, functional activity against 5 of the 7 PSs was demonstrable, both in vitro and in vivo. Recurrent pneumococcal bacteremia in patients who have undergone splenectomy may indicate a genetically regulated failure to respond to PPV-23; PCPV-7 may stimulate production of IgG to PSs in such patients. © 2005 by the Infectious Diseases Society of America. All rights reserved.