beta-Phenylethylamine (PEA) was detected and quantitated in tissues of the catfish, Parasilurus asotus, by very specific and sensitive gas chromatography/mass spectrometry. 2. The selected ion monitoring was made with a strong quasi-molecular ion of the pentafluoropropionic derivative of PEA in the positive chemical ionization mode. 3. PEA was found in all tissues tested ranging from 2.8 to 38.2 ng/g wet wt tissue. It was highest in the spinal cord, followed by the skin, brain and intestine.