Developmental regulation of the diversity of the antibody repertoire is associated with the controlled stepwise acquisition of Ag responsiveness during ontogeny. The development of IgG and IgA serum levels in humans lags far behind the maturation of the rest of the immune response. We cloned cord blood mononuclear cell Cγ and Cα transcripts and compared them with a large database of >250 published and unpublished sequences, including Cμ transcripts from this same cord blood cDNA library, to determine whether restrictions in the expressed antibody repertoire contributed to the limitations of the neonatal IgG and IgA response. We found a diverse antibody repertoire containing a high frequency of the same V(H) gene segments first identified in fetal liver, as well as V(H) elements homologous to those in the cord blood Cμ transcripts. Although V(H), D(H), and J(H) utilization differed, the distribution of CDR3 lengths in the Cγ transcripts was similar to that found in fetal liver Cμ transcripts, whereas the distribution of CDR3 lengths in the Cα transcripts was similar to that found in cord blood Cμ. This comprehensive analysis of the Cμ, Cγ, and Cα V domain repertoires provides new insights into our understanding of the timing of sequential B cell waves that seed peripheral lymphoid compartments during development.