Chromosomal arm 1p has long been suspected, on the basis of loss of heterozygosity (LOH) and other data, to harbor a tumor suppressor gene important in pancreatic carcinomas and other tumors. We constructed a high-resolution map of LOH at I p in a panel of pancreatic adenocarcinomas. Using 44 markers, we identified LOH on I p in 49% of 43 cancers. Breakpoints in 1p were identified in 15 of the carcinomas and could be used to ascertain consensus patterns. We found a major consensus region of LOH at 1p35 between loci D1S233 and D1S247. This region participates in the majority of LOH events on 1 p in pancreatic cancer. These data provide a roadmap for further regional mapping, homozygous deletion searches, comparison to LOH patterns seen in other tumor types, and prioritization of studies using candidate genes.