We have recently found that Tokishakuyakusan (TS), Keishibukuryogan (KB) or Unkeito (UT) inhibits in vivo DNA polymerase alpha activity in the rat uterus stimulated by PMS. In this study, uteri resected 24 h after injection of PMS on day 27 of age were incubated in vitro with 20 micrograms/ml of extract of TS, KB or UT for 4 h. The DNA polymerase alpha activity in uteri tended to decrease after the addition of TS, KB or UT with significant difference (P < 0.05) compared with TS-, KB- and UT-untreated control groups. These results suggest that TS, KB or UT, especially KB, tends to inhibit directly the enzyme activity in rat uterus.