This part of ISO 23893 specifies a method for measuring the ethoxyresorufin-O-deethylase (EROD) enzyme activity on a post-mitochondrial fraction of fish liver homogenate (subcellular fraction in which the EROD activity is located) employing a cell or microplate fluorimetric method. It applies to fish that are sampled in their natural environment (fresh water or salt water) or exposed to substances or effluents in a laboratory. This method is applicable for EROD values greater than or equal to 1 pmol/(min·mg) of proteins. A higher sensitivity may be achieved by using a cell (test tube) procedure