A new method of continuous culture with selective bleeding of mycelia using 9-mesh screen was developed to improve the production rate of peroxidase (POD) by Arthromyces ramosus. At the dilution rate of 0.05 h(-1) with the mycelium leakage rate of 60%, a high production rate (average value was 1.67 U . ml(-1). h(-1)) was maintained for over 100 h : the rate was 3.2 times that in a glucose-fed batch culture. At the same dilution rate, the volumetric and specific production rates of POD in the continuous culture without the screen were lower than those in the first continuous culture and decreased gradually in the later phase of the culture. In the continuous culture with low mycelium leakage rate of 1.6%, the POD production rate was not improved further, although the mycelial concentration (43 g . l(-1)) increased 2.9 times. It is suggested that the high agitation rate required to meet the oxygen demand is unfavorable for the POD production.