Recently, i(8q) was suggested to be a nonrandom chromosomal abnormality characteristic of adenocarcinoma of the lung. To further investigate this observation, a chromosomal analysis of five cases of pleural effusions representing metastatic adenocarcinoma from different primary sites (two lung, two breast, and one stomach) was undertaken. The i(8q) occurred in three of the tumors, one from each of the three different primary sites. In addition, abnormalities of the short arm of chromosome 3 and extra copies of chromosome 7, both of which have been associated with adenocarcinoma of the lung, were simultaneously present in the same three tumors. Our findings demonstrate that i(8q) is not specific for adenocarcinoma of the lung and that it may have a role in the pathogenesis of adenocarcinomas from multiple organs. The simultaneous presence of i(8q), abnormalities of 3p, and extra copies of chromosome 7 may indicate a relationship among these abnormalities in multistep carcinogenesis or the development of metastatic potential.