Among 46 species of fungi isolated from decaying Ocotea wood, growth differed in response to oxygen stress during a 24 d trial. All fungi grew for one week but during the following 17 d, six different growth responses emerged. In 12 species daily growth rates were initially stimulated, then totally inhibited; in 4 high growth rates were maintained over the 24 d period; in 5 growth rates were similar under both aerobic and anaerobic conditions and then stopped under the latter; in 5 growth rates in both treatments were similar during the whole trial period; in 16 growth was retarded before inhibition, and in 4 growth was retarded without being inhibited. Growth of 91% of the fungi able to produce ligninolytic enzymes was significantly inhibited or retarded in the absence of oxygen. The behaviour of the fungi under oxygen stress conditions is discussed regarding their roles in the colonization and decay of stems of standing Ocotea trees. It is concluded that in standing trees, oxygen stress may exert selective pressure during successive colonisation, and that tolerance to oxygen stress favours Phellinus species and Loweporus inflexibilis in becoming the main climax decay species in Ocotea trees.