The consistency of the breakpoint on chromosome 5 at band 5q35 occurring in Ki-1 non-Hodgkin's lymphomas is highly suggestive of the involvement of a locally altered gene in this disease. In this study, we analyzed the potential involvement, in the translocation, of two receptor tyrosine kinase genes and putative oncogenes, FLT4 and FGFR4, previously localized near this breakpoint. Fluorescence in situ chromosomal hybridization allowed us to refine their localization to sub-band 5q35.3 and to show that both genes are translocated to the derivative chromosomes in Ki-1 cell lines containing either a t(2;5) or a t(3;5). Pulsed-field gel electrophoresis showed that the FLT4 and FGFR4 genes are not physically linked, nor are they altered by the translocation. Finally, Northern blot analysis showed that neither FLT4 nor FGFR4 is expressed in the Ki-1 cell lines, suggesting that they are not implicated in the genesis of Ki-1 lymphomas.