Flow cytometry (FC) analysis including DNA index (ploidy status) and cell kinetics (%S and %S + G2/ M) was done on frozen tissue of the primary lesions of 101 women with node negative (N-) breast cancer who were studied prospectively . Currently, 19% (19/101) of the patients have recurred. No significant relations have been found between recurrence or survival and age, estrogen/progesterone receptor status, tumor size, and tumor type. The DNA index (ploidy) was not related to any clinical variable, time to recurrence, or survival. Aneuploid tumors did, however, have significantly higher %S phase activity. Patients with %S activity less than or equal to the median value were significantly different from those patients with %S above the median. They were older and had a higher frequency of ER/PR positive and well-or moderately differentiated tumors. Patients with %S + G2/M greater than the median value showed shorter time to recurrence (P = .055) and shorter survival (P = .006), whereas %S alone was significantly associated only with survival. Multivariate analysis showed that neither DNA index nor cell kinetics was significantly associated with time to relapse. DNA index was not significantly associated with survival; %S was of borderline significance whereas %S + %GJM was a significant independent predictor of survival. Although FC data may provide independent information related to survival in Nwomen, additional research in a larger number of patients is needed to define its precise role in patient management.