Application of the Maxblend(R) impeller to the fermentative production of hyaluronic acid (HA) was investigated. A 2-m(3)-scale fermenter fitted with this impeller (MBF) was used and the main fermentation was started with 85% of the nominal volume containing the pre-culture broth and medium. The kinetic characteristics of the MBF were compared with those of a conventional-type fermenter fitted with a turbine blade (TBN). The HA production yield in the MBF was over 20% higher than that in the TEN under the operating conditions of a high aeration rate and low vessel pressure since the broth viscosity increased. The apparent viscosity of the broth at the end of the cultivation rose to about 70 Pa.s. The molecular weight of the HA produced was independent of the agitation speed within the investigated range, and no significant difference was observed between the viscosity-average molecular weights of the HA obtained in the two types of fermenter, each having an estimated value of 4.3 x 10(6) under the same agitation power.