We examined the repertoire of antibodies to Streptococcus pneumoniae 6B capsular polysaccharide induced with the conventional polysaccharide vaccine in adults at the molecular level two ways. In the first, we purified from the sera of seven vaccinees antipneumococcal antibodies and determined their amino acid sequences. Their VH regions are mainly the products of VH3 family genes (candidate genes, 3-23, 3-07, 3-66, and 3-74), but the product of a VH1 family gene (candidate gene, 1-03) is occasionally used. All seven individuals have small amounts of polyclonal κ+ antibodies (Vκ1 to Vκ4 families), although κ+ antibodies are occasionally dominated by antibodies formed with the product of the A27 Vκ gene. In contrast, λ+ anti-6B antibodies are dominated by the antibodies derived from one of 3 very similar Vλ2 family genes (candidate genes, 2c, 2e, and 2a2) and Cλ1 gene product. The Vλ2+ antibodies express the 8.12 idiotype, which is expressed on anti- double-stranded-DNA antibodies. In one case, Vλ is derived from a rarely expressed Vλ gene, 10a. In the second approach, we studied a human hybridoma (Dob1) producing anti-6B antibody. Its VH region sequence is closely related to those of the 3-15 VH gene (88% nucleotide homology) and JH4 (92% homology). Its VL region is homologous to the 2a2 Vλ2 gene (91%) and Jλ1/Cλ1. Taken together, the V region of human anti-6B antibodies is commonly formed by a VH3 and a Vλ2 family gene product.