Recent studies have suggested the existence of one or several tumor-suppressor genes on chromosome arm 1p in colorectal tumors. To determine the localization of the putative tumor suppressor genes, we performed LOH analysis in 1p in colorectal tumors. A total of 48 paired normal and tumor DNAs of 46 colorectal tumor patients and 21 microsatellite markers on 1p32.1-p36.3 were used for PCR-LOH analysis. Three commonly deleted regions were found: i) 1p36.3 (10-cm); ii) 1p35.1-p36.3 (2-cm); and iii) 1p34.2-p35 (1-cm). These regions overlapped with those reported in several types of tumor. No significant associations were found between LOH and clinicopathologic features. The regions identified in the present study could harbor tumor suppressor genes that would also be associated with several types of human cancer.