The immune system produces a vast repertoire of immunoglobulins (Ig) in response to the wide number of different antigens to which we are exposed. Thanks to processes such as V(D)J recombination, somatic hypermutation, and antigen selection, the immune system is able of generating the high diversity of Ig sequences. Igs are present in the body as soluble or membrane-bound proteins attached to the B-cells (similar structure to IgM) for regulating the immune system and performing the function of B-cell receptors (BCR), respectively. Specifically, the disrupted activation of the BCR appears as the responsible of the chronic lymphocytic leukemia (CLL). We have focused this study in the sequencing of cellular Ig from B cells purified from the peripheral blood of CLL patients in order to characterize their peptide profiles.