PRAD1 (parathyroid adenoma 1) gene at chromosome 11q13 has been cloned from parathyroid adenomas as a putative oncogene, activated by translocation with the parathyroid hormone gene. 4.5 kb and 1.7 kb mRNA are transcribed and both have the same open reading frame of 885 bp encoding 34 kd protein of a cyclin gene family, cyclin D1. Recently, overexpression of PRAD1 gene has been reported to be correlated closely with the rearrangement of bcl-1 locus, particularly in centrocytic lymphoma. In our study, overexpression of PRAD1 gene was shown in five B cell lines with t(11;14)(q13;q32) including one centrocytic lymphoma line and 4 myeloma lines, when compared with other hematopoietic cell lines without translocation. One of the cell lines, SP-49, demonstrated a truncated mRNA of 3.4 kb, in addition to 1.7 kb of normal size. Southern blot analysis demonstrated a rearrangement with PRAD1 cDNA probe, suggesting that the gene is altered in this particular cell line. By cloning analysis, we confirmed that 1.8 kb deletion in 3' region of PRAD1 gene eliminating the destabilizing signal of PRAD1 mRNA, gave rise to the aberrant mRNA of 3.4 kb. These findings suggest that PRAD1 gene is most likely the candidate oncogene for bcl-1 activated by t(11; 14)(q13;q32) translocation. The gene alteration found in one cell line, SP-49, might also play an important role for deregulation of the gene.