Seven strains of Emericella nidulans were isolated from lesions in the guttural pouch of horses with mycosis of this pouch. All strains grew in a wide range of temperature, pH and in five kinds of culture media. The optimum temperature that supported their growth was 38 degrees C, and all seemed to prefer an acidic environment with a pH of 4.0. Proliferative conidial formation was found to be induced by the aforementioned temperature and pH. Moreover, detection of beta-haemolysis and protease production suggested that these strains are biologically and biochemically active, which may imply that they have a potent pathogenicity of their own. Characteristics of two other strains of E. nidulans isolated from fomites were the same as those isolated from the infected horses. These findings suggest that E. nidulans is a potentially pathogenic to horses.