We report detailed chromosome banding analysis of six cases of ovarian adenocarcinoma cultured 24--96 hr in a recently developed bioassay for clonogenic tumor cells. The results of G and C banding revealed a variety of chromosome changes including the observation of a simple deletion for a portion of the long arm of chromosome #6, del(6)(pter leads to q15--21:), in tumor cells from four of six patients. Our study indicates that short-term agar culture can provide a valuable tool in the study of tumor cell karyology. A comparison of our results with previously published studies suggests that in addition to alterations of chromosome #1, the deletion of 6q may represent a characteristic chromosomal aberration in ovarian carcinoma.