Molecular analyses for loss of heterozygosity (LOH) at a gene locus are used to identify genomic imbalance in tumor tissue. A frequently utilized microsatellite marker for the Adenomatous Polyposis Coli (APC) gene is denoted D5S346. However, when an individual has two identical forms of this microsatellite, then a second microsatellite, also near the APC gene, is needed. We present data on an APC microsatellite marker designated D5S1385, located on the 5' end of the APC gene, and we compare these to data utilizing the marker D5S346. Polymerase chain reaction (PCR) was used, followed by gel electrophoresis. Homozygosity for the marker D5S1385 was present in 55 individuals, or 28%. Thirty-seven carcinomas and 32 adenomas were assessed for LOH from individuals informative with both microsatellite markers. D5S1385 detected LOH in 39 of 41 lesions, or 95%, for which D5S346 detected LOH. D5S1385 is moderately polymorphic and is informative at least as often as D5S346.