SummaryThe ERBAB gene codes for a DNA-binding thyroid hormone receptor (THR) and maps to chromosome 3p21-p25, overlapping a 3p deletion characterizing small-cell lung carcinoma (SCLC). A DNA clone detecting an RFLP at the ERBADi locus has been used to probe a large number of lung tumors. Virtually all SCLC had lost heterozygosity, showing that the 3p deletion in SCLC includes this gene. A substantial but smaller proportion of non-small-cell carcinomas had lost heterozygosity at ERBAB. Among all non-smallcell tumors some had lost heterozygosity at the proximal locus DNF15S2 (band 3p2l) but not at ERBADi, whereas none were found where the reverse was true. Therefore, the locus which plays a role in non-smallcell tumorigenesis probably lies closer to DNF15S2 than to ERBAB and is almost certainly not the latter.