This part of ISO 15181 specifies a method for determining the amount of tralopyril that has been released from an antifouling paint into artificial seawater in accordance with the procedure given in ISO 15181-1. Tralopyril is unstable in water and degrades hydrolytically to form 3-bromo-5-(4-chlorophenyl)-4-cyano-1H-pyrrole-2-carboxylic acid (BCCPCA). This part of ISO 15181 specifies a method for accelerating the conversion of the released tralopyril into this degradation product by heat treatment and quantifying the concentration of the BCCPCA degradation product in the artificial seawater extract, and gives the final calculation for the release rate of tralopyril under the specified laboratory conditions. This part of ISO 15181 is designed to allow the concurrent determination of tralopyril and other biocides that can be released by a given antifouling paint (for example, zineb) through the analysis of separate sub-samples of an artificial seawater extract generated in accordance with ISO 15181-1. When used in conjunction with ISO 15181-1, the practical limits for quantifying release rates by this method are from 0,36 µg cm−2 d−1 to 270 µg cm−2 d−1. The quantitation of release rates lower than this range requires the use of an analytical method with a limit of quantitation for tralopyril in artificial seawater of less than 2 μg/l.