We report the complete variable region sequences of three homogeneous rabbit antibody light chains and the partial sequences of five others. Wehn these are compared to other published rabbit light chain sequences, two regions of markedly increased variability are revealed, which are homologous in position to the first and third hypervariable regions of murine and human myeloma light chains. In addition, there is increased variability among the first three residues at the aminoterminal end. A hypervariable region homologous to that identified at positions 50 to 56 in myeloma light chains is not present in these rabbit antibody light chains. The available three-dimensional models of Fab fragments based on x-ray crystallography indicate that neither the amino-terminal portion of the light chain nor the region homologous to positions 50 to 56 forms a part of the combining site. Comparison of the hypervariable regions among six light chains from antibodies to Type III pneumococcal polysaccharide and among four from antibodies to Type VIII pneumococcal polysaccharide suggests that a large number of different sequences may be found in antibodies specific for these relatively simple antigens. Certain residues outside of the hypervariable regions are invariant in the rabbit light chains and correspond to residues that are required for proper chain folding in human and murine myeloma light chains, indicating that the general conformation of myeloma light chains is the same as that of light chains of elicited antibodies.