PURPOSE: The aim of this study was to compare the S-phase fraction (SPF) and Ki-67 with other biologic factors, and to assess the prognostic value of Ki-67 and SPF in 108 breast cancer patients. MEHOODS: The SPF and Ki-67 level were determined in formalin-fixed, paraffin-embedded tissue specimens from 108 patients with early breast cancer who underwent surgery between January 1997 and December 2000 at the Wonkwang University Hospital. The clinicopathological characteristics of the early breast cancer such as the tumor size, node status, histological grade, hormone receptor, various tumor markers and cancer recurrence were compared with the SPF and Ki-67 values. RESULTS: The median SPF was 9.03% (range 0~43%). The SPF correlated with CD31 (P=0.020) and DNA diploidy (P=0.000). Ki-67 correlated with the histological grade (P= 0.010) and p53 (P=0.035). No correlation was found between the SPF and Ki-67. Eight cases recurred during the follow-up period. Strong expression of Ki-67, p53, DNA aneuploidy and a young age were correlated with recurrence (P=0.001, P=0.029, P=0.021 and P=0.002, respectively). However, the SPF was not related to recurrence. CONCLUSION: In early breast cancer, Ki-67 expression is correlated with the histological grade and p53 expression. In addition, strong Ki-67 expression is associated with a recurrence. Further studies regarding the prognostic significance of the proliferation markers, such as Ki-67 and SPF, will be needed to confirm these results.