Background.Pneumococcal conjugate vaccines are intended to provide effective protection against pneumococcal infections, but very little information on antibody responses in infants living in countries with high pneumococcal disease burden exists.Methods.In this study 50 healthy Filipino infants were enrolled at a village health center in Cabuyao to receive 11-valent diphtheria- and tetanus-conjugated pneumococcal vaccine at 6, 10 and 14 weeks of age (primary series) simultaneously with diphtheria-tetanus-whole cell pertussis/polyribosylribitol phosphate conjugated to tetanus toxoid, hepatitis B virus and oral poliovirus vaccines and at 9 months of age (booster dose) simultaneously with measles vaccine. The alum-adjuvanted study vaccine contained pneumococcal polysaccharide of serotypes 1, 4, 5, 7F, 9V, 19F and 23F conjugated to tetanus protein and pneumococcal polysaccharide of serotypes 3, 6B, 14 and 18C conjugated to diphtheria toxoid. Serum samples for enzyme immunoassay analyses were collected at 6, 10 and 14 weeks and 9 and 10 months of age.Results.Very high geometric mean antibody concentrations (GMCs) against most pneumococcal serotypes were observed after the first three doses of vaccine (range, serotype 23F, 3.89 &mgr;g/ml to serotype 4, 23.41 &mgr;g/ml) with the exception of serotype 6B and 14, with GMCs of 1.12 and 2.18 &mgr;g/ml, respectively. The fourth dose increased the GMCs against most serotypes (range, serotype 14, 1.65 to serotype 19F, 33.43 &mgr;g/ml). The maternally derived antibodies did not decrease the response to the vaccine.Conclusions.This first pneumococcal conjugate vaccine study in Asia confirms that the 11-valent diphtheria- and tetanus-conjugated pneumococcal vaccine is highly immunogenic in Filipino infants. The GMCs against most pneumococcal serotypes were substantially higher than described with the same or other pneumococcal conjugate vaccines in other populations.