Diuse large B-cell lymphomas (DLBL) constitute an heterogeneous clinico-pathological entity. To characterize molecular events related to histological subtypes, clinical presentation or outcome, we compared the mRNAs expressed in a limited series of DLBL by Dierential display-reverse transcription (DDRT) and cloned a dierential cDNA, that we called LB1. LB1 open reading frame encodes a 683 amino-acid polypeptide that does not show signi®cant homology upon comparison to protein databases, nor any structural domain relating LB1 to an already known protein family. Immuno¯uorescence analysis of transfected COS cells showed a cytoplasmic ®lamentous staining, indicating that LB1 protein is tightly associated with cytoskeletal ®bers. Two LB1 transcripts, a major 3.6 ± 3.9 Kb and a minor 2.2 Kb transcripts, were detected among human haematopoietic and non-haematopoietic lines and tissues. LB1 transcripts were abundant in testis, thymus and in tumour derived cell lines, while barely detectable in liver, prostate and kidney. Concerning DLBL, LB1 expression was high in two cases of DLBL, and low or undetectable in four others, con®rming the dierential expression previously observed in the DDRT experiment. Furthermore, LB1 gene mapped to chromosome 13q14, a region that has been involved as a chromosomal breakpoint in DLBL. The cellular function of LB1 and its relationship with B cell maturation and/or oncogenesis remain to be established.