The FHIT (fragile histidine triad) gene is located in the chromosomal region 3p14.2 and encodes a 16.8 kDa member of the HIT superfamily of nucleoside monophosphate hydrolases and transferases. The 1.6 Mb FHIT gene encompasses the most carcinogen-sensitive common fragile region FRA3B and the t(3;8) translocation breakpoint associated with hereditary renal carcinoma. The tumor suppressor gene FHIT is inactivated by deletions in a variety of human tumors e.g. lung, kidney, gastric, breast, pancreatic, and cervical tumors. Since loss of the FHIT locus occurs in a number of preneoplastic lesions, FHIT may represent a potential marker for the detection of tumor precursor cells. FISH probes can be used for for the detection of FHIT gene deletions frequently observed in most of the common epithelial neoplasms.