Concurrent Cloning Efficiencies (CE) of both ascites and solid tumor samples from 36 patients with ovarian carcinoma were studied using the soft agar assay. The CE of both were highly variable (range, 0-1.234% and 0-0.802%, respectively). There was marked intrapatient and interpatient heterogeneity in the CE. Of the 36 tested, comparative CE were evaluable in 29. CE was 0 in both solid tumor and ascites in one patient. CE was 0 in four other ascites samples from four patients. In other 24, the relative CE of solid tumor/ascites from each patient ranged from 0.066 to 435. In the 29 patients with samples of ascites and a solid tumor evaluable for concurrent CE, the median colony counts of solid tumors was more than tenfold higher than ascites. The solid tumors obtained from 31 patients had a significantly higher CE than tumor cells obtained from ascites samples from 32 patients. Solid tumors were significantly better than ascites for in vitro testing based on the data that 75% (27/36) of solid tumors and only 31% (11/36) of ascites formed greater than or equal to 30 colonies. The drug sensitivity profiles of tumor cells from a solid tumor and ascites of the same patient appear similar. Based on these observations, it may be more cost and labor effective to do soft agar in vitro chemotherapy assays using a solid tumor than ascites in ovarian carcinoma.