The significance of Mn and Fe for the growth of a coastal marine diatom Thalassiosira weissflogii was investigated by performing culture experiments containing macronutrients with either Mn or Fe, or both. Only the addition of both Mn and Fe induced the highest growth rates and maximal cell yields. Maximal growth was maintained in continuous culture media, which were repeatedly prepared by an inoculation of pre-culture and the addition of both Mn and Fe to the control culture medium containing macronutrients. In particular, it was found that the full growth recovery in Mn-sufficient medium (without added Fe) is accomplished by the addition of Fe even after several days' incubation. On the contrary, there was no sufficient growth recovery by the addition of Mn after a long incubation time in Fe-sufficient medium but without additional Mn. These results suggest that T. weissflogii in Mn-sufficient waters retains the ability for full physiological recovery for a long time, probably resulting from the decrease in the oxidative stress of phytoplankton by the production of antioxidant enzyme Mn superoxide dismutase during a long incubation period.