This method describes procedures for using high performance liquid chromatography (HPLC) and inductively couple plasma-mass spectrometry (ICP-MS) to determine methylmercury and total mercury in seafood. Total mercury in this method is calculated as the sum of inorganic and methylmercury determined in analytical solution. Other matrices may be analyzed by these procedures if performance is verified in the matrix of interest, at the concentration levels of interest. The limits listed in 4.8 Table 1 are intended as a guide and actual limits are dependent on the sample matrix, instrumentation and selected operating conditions.