Pleurotus ostreatus No. 42 produced the ligninolytic enzymes, manganese peroxidase (MnP) and laccase, in agitation culture in glucose/peptone/wheatbran medium. Formation of mycelial pellets 1-2 mm in diameter was essential for the production of MnP: and the concentration of dissolved oxygen in the culture medium greatly influenced the production of MnP, a concentration over 5 ppm being necessary for MnP production. The maximal activity of MnP was obtained on days 7-9 of culture, after the consumption of nutrient glucose. Introduction of oxygen from the start of the cultivation caused large pellet formation, which resulted in a low MnP activity level. P. ostreatus No. 42 produced two MnP isozymes in agitation culture. The major isozyme, F-2, was 36.4 kDa and had a pi of 3.95. The MnP characteristics, K, values, dependence on Mn2+ and optimum pH showed the similarity between this isozyme and MnP 3, which was produced under different culture conditions. Analysis of the N-terminal amino acid sequence indicated the close similarity of F-2 to MnP 3.