A procedure for the quantitative evaluation of p-tyramine in mammalian tissues is described. It involves isolation of the amine by ion-exchange chromatography, followed by conversion to the dansyl derivative, chromatographic separation, and quantitation by the mass spectrometric integrated ion current technique using an isotopically labelled internal standard.The concentrations of p-tyramine in some tissues of male Wistar rats were (mean ± standard deviation (ng/g)): brain 2.0 ± 0.9, heart 3.4 ± 1.4, kidney 32.7 ± 13.1, liver 1.5 ± 0.5, lung 3.0 ± 1.2, and spleen 3.4 ± 1.2. In the brain, hypothalamus contained 11.3 ± 3.7, cerebellum 2.3 ± 1.7, stem 2.2 ± 1.0, caudate nucleus 19.2 ± 2.5, and the 'rest' 1.6 ± 0.4 ng/g, respectively.