The cell cycle of Familial Polyposis Coli (FPC) has been determined by a flow cytometric (FCM) DNA/bromodeoxyuridine (BrdUrd) bivariate analysis. Specimens were obtained from one FPC cancer patient and, for our controls, from 8 single colon cancer patients and from 8 gastric cancer patients who underwent a colectomy. Procedurally, 1 g i.v. injection of BrdUrd was administered 5 to 7 hours before the resection. Later, the BrdUrd-labeling index (BULI) and the potential doubling time (Tpot) were measured by FCM. No significant differences were uncovered between the BULI of the cancer in the FPC patient and that of our controls, or between the BULI of the unaffected mucosa of the FPC patient and that of the controls. Further, with regard to the FPC patient, the mean BULI of the cancer was significantly higher than that of the adenoma and than that of the unaffected mucosa. Also, the mean Tpot of the cancer was significantly shorter than that of the unaffected mucosa. These results suggest that the BULI and the Tpot may change when an adenoma is generated from the unaffected mucosa in FPC patients.