We demonstrate that the cytogenetically defined translocation t (X; 1)(p11. 2; p34) observed in papillary renal cell carcinomas results in the fusion of the splicing factor gene PSF located at 1p34 to the TFE3 helix–loop–helix transcription factor gene at Xp11. 2. In addition we define an X chromosome inversion inv (X)(p11. 2; q12) that results in the fusion of the NonO (p54 nrb) gene to TFE3. NonO (p54 nrb), the human homologue of the Drosophila gene NonA diss which controls the male courtship song, is closely related to PSF and also believed to be involved in RNA splicing. In each case the rearrangement results in the fusion of almost the entire splicing factor protein to the TFE3 DNA-binding domain. These observations suggest the possibility of intriguing links between the processes of RNA splicing, DNA transcription and oncogenesis.