Gastric cancer is one of the leading causes of death from cancer throughout the world, and studies to elucidate the genetic defects found in this type of cancer are growing in number. Increasingly sophisticated techniques and the sequencing of the human genome have had an impact on the scope of such studies. While the use of tumor specimens remains popular, more emphasis is being placed on cell lines as model systems where specific data can be directly combined with results from other studies. This article describes a genetic survey of the most widely used gastric adenocarcinoma cell lines. The allelotype at 351 polymorphic loci in 14 cell lines was obtained, and the results from the 4,900 polymerase chain reactions are displayed. In addition to confirming loss of heterozygosity on chromosome arms 6p, 7q, 17p, and 18, additional deletions on arm 5p and the pericentromeric regions of chromosomes 1 and 10 were detected. Areas that might contain homozygous deletions or amplifications also were mapped. The rate of microsatellite instability was quantified and shown to vary greatly among the different cell lines. Most important, this study serves as a genetic scaffold for the integration of past and future studies on the nature of the genetic defects in gastric cancer.