Loss of heterozygosity (LOH) studies have emerged as a valuable indicator for tumor suppressor genes involved in the formation or progression of carcinomas. We here present data indicating that human chromosome 15 harbours a novel putative tumor suppressor gene which appears to play a role during later stages of carcinogenesis and which may be associated with metastasis in breast cancer. In this study, 153 primary and metastatic carcinomas from 101 patients have been analysed for LOH with 13 polymorphic microsatellite markers on chromosome 15. The tumors included carcinoma of the lung in 49 patients, breast carcinoma in 29, colorectal carcinoma in nine, renal carcinoma in five, pancreatic carcinoma in five, urinary bladder carcinoma in two and prostate carcinoma and ovarial carcinoma in one patient each. LOH15 was seen in 42/99 (42%) informative patients. In metastatic tumors, LOH15 was observed in 37/68 (54%). High incidences of allelic losses were detected in metastases from lung (56%), breast (70%) and colorectal (67%) carcinomas. In carcinomas of the breast, there was a significant difference (P<0.01) in LOH15 frequencies between non-metastatic tumors (11%) and brain metastases (70%). Such a difference was not observed on the chromosomal arm 17p which yielded high proportions of LOH in both non metastatic breast tumor (73%) and breast carcinoma metastases (90%). In 16 patients, interstitial deletions could be detected. The common region of overlap extended from D15S231 to D15S641, thus mapping this putative tumor suppressor gene to chromosome 15q14. Our data indicate that a gene on chromosome 15 contributes to the pathogenesis of metastatic carcinoma.