To gain insight into the mechanisms underlying VH CDR3 restrictions and also determine the developmental stage when restrictions in VH CDR3 are imposed, we analyzed partial IGHD-IGHJ rearrangements (D-J) in 829 CLL cases and compared the productively rearranged D-J joints (that is, in-frame junctions without junctional stop codons) to (a) the productive immunoglobulin heavy variable (IGHV )-IGHD-IGHJ rearrangements (V-D-J) from the same cases and (b) 174 D-J rearrangements from 160 precursor B-cell acute lymphoblastic leukemia cases (pre-B acute lymphoblastic leukemia [ALL]).