Recently several chromosomal translocations involved in myeloma cases and myeloma cell lines; ie, t (11; 14)(q13; q32), t ('8; 14)(q24; q32), t (4; 14)(q16. 3; q32. 3), t (6; 14)(p25; q32), and t (14; 16)(q32. 3; q23), have been identified. These translocations are considered to dysregulate genes which may be concerned with myelomagenesis; ie, PRAD1/cyclin D1, the c-myc oncogene, FGFR3 (fibroblast growth factor receptor 3), MMSET (multiple myeloma SET domain), MUM1 (multiple myeloma oncogene 1)/IRF4 (interferon regulatory factor 4), and the c-maf oncogene, respectively. However, the cellular biological roles of these genes have not yet been elucidated in myeloma cells. Because two of the seven human myeloma cell lines which were established at Kawasaki Medical School, Okayama, Japan, KMS-11 and KMS-18, have been proven to possess t (4; 14)(q16. 3; q32. 3), we studied the expression levels of the FGFR3 gene in these seven cell lines and 13 primary myeloma specimens. The expression levels of 12 known FGF family genes (FGF-1 to 12) and 4 FGFR genes (FGFR1 to 4) were also examined in seven cell lines. In addition, the growth status of the KMS-11 and KMS-18 lines with FGF-1 or anti-FGF-4 neutralizing monoclonal antibody (MoAb) supplementation was investigated because FGF-1 and 4 are known as the principal ligands for FGFR3. FGFR3 overexpression was observed in both of the cell lines possessing t (4; 14)(q16. 3; q32. 3) and in 3 of 13 case specimens. Anti-FGF-4 neutralizing MoAb caused significant growth inhibition in these two cell lines possessing t (4; 14)(q16. 3; q32. 3). These findings indicate that t (4; 14)(q16. 3; q32. 3) may provide myeloma cells with a growth advantage via an autocrine mechanism between FGFR3 and FGF-4.