Domoic acid is extracted from mussel tissue using the Association of Official Analytical Chemists procedure for paralytic shellfish toxins. This involves boiling the sample for 5 min with O.1N HCl then cooling and centrifuging. An aliquot of the supernatant is diluted 10 to 100 times with water, filtered and analyzed by reversed-phase liquid chromatography with a mobile phase of acetonitrile-water (12:88) at pH 2.5 and absorption detection at 242 nm. The detection limit is about 1 mg/kg domoic acid in seafood samples. The method was successfully used in collaborative studies and a survey of 44 different commercially purchased shellfish products from areas outside of Prince Edward Island showed no domoic acid greater than 1 mg/kg. The same method was applied to urine and feces from monkeys and blood (serum) from humans. The method was unsuccessful for urine and blood which required additional cleanup before analysis. The method worked well for feces at domoic acid levels greater than 1 mg/kg.