The human pre-B acute lymphoblastic leukemia cell line, BLIN-1, has been previously shown to undergo κ light chain rearrangement in vitro, making it a valuable resource for analyzing pre-B to B cell differentiation. We have examined the recombination potential of BLIN-1 by characterizing several independently derived κ-expressing subclones for DNA rearrangement and Vκ gene usage. Analysis of five κ-expressing subclones (all having the same heavy chain rearrangement) demonstrated independent κ light chain rearrangement events by DNA hybridization analysis. Northern blot analysis using probes recognizing the four different V(κ) families revealed that two subclones used the most proximal V(κ) (V(κ)IV), one subclone used a VκI, and one subclone used a V(κ)II. By polymerase chain reaction analyses, we detected transcripts from rearranged V-J-C(κ) genes as well as transcripts from germline J-C(κ) and V(κ) in BLIN-1 cells induced to rearrange the κ locus. κ germline transcripts were also detected in normal developing B cell populations in fetal liver and bone marrow. Our collective results indicate that: (a) BLIN-1 can be induced to rearrange the κ locus, and this correlates with the expression of germline κ locus transcripts that may play a role in activating or targeting gene rearrangement; and (b) active rearrangement and usage of V genes representing different κ families suggest that, like in the mouse, repertoire diversification in humans occurs in the presence of a fixed heavy chain rearrangement.