The growth of gut anaerobic fungi is usually determined in batch culture by gravimetric measurements of dry-matter (DM) loss, or by quantification of fermentation end-products (Lowe et al., 1987). These techniques involve destructive sampling of the cultures and require many replicate cultures in time-course experiments. Moreover, techniques using DM loss are only able to measure the end-point of degradation of substrate and cannot follow the growth over the entire fermentation period. Using a pressure transducer, Theodorou et al. (1994) developed a simple and sensitive gas production procedure to determine the fermentation kinetics of ruminant foods. This procedure can also be used to follow the growth of anaerobic fungi on soluble and particulate substrate in batch cultures Theodorou et al. (1995).