FHIT is a putative Human tumor suppressor gene at chromosome 3p14.2 that was identified recently by positional cloning. Homozygous deletions within the FHIT locus have been observed in cell lines derived from cancers of the esophagus, stomach, colon, breast, kidney, and lung, and aberrant transcripts were observed in several types of primary tumors. This gene also encompasses the site of the t (3; 8) translocation breakpoint of familial renal clear cell carcinoma and the fragile site locus FRA3B. The1.1-kb FHIT cDNA is encoded by 10 small exons distributed over a genomic locus of about 1 Mb; the t (3;8) break falls between untranslated 5' exons 3 and 4. The protein is a dinucleoside 5', 5