Translocations involving the long arm of human chromosome 19 are specific chromosomal alterations found in a subset of benign thyroid tumors. In the present communication we describe the establishment of an SV40-transformed cell line derived from a thyroid adenoma with a t(1;19)(p35 or p36.1;q13). Cytogenetic studies were carried out on this cell line, using a series of cosmids mapping along the long arm of chromosome 19. In situ hybridization with probes for RYR1, ATP1A3, BCKDHA, ERCC1, POLD1, and TRPT revealed that only TRPT mapped distal to the breakpoint of the translocation. The results indicated that the breakpoint is located between POLD1 and TRPT at the boundary between chromosome bands 19q13.3 and 19q13.4.