Some species of the genus Phalaris used as forage in many regions of the world induce particu­lar toxic syndromes in Iivestock. The most interesting among these syndromes are the neurologi­cal acute and the chronic kinds, named "Phalaris staggers». Most authors consider them as a uni­que syndrome, (partially) caused by indole alkaloids found in P. arundinacea and P. aquatica: gra­mine, N,N-dimethy!tryptamine, N-methyl-tryptamine, 5-hydroxy-dimethy!tryptamine (bufote­nine), 5-methoxy-dimethyltryptamine, 5- methoxy-methyltryptamine and others. We can add to these alkaloids the beta-carbolines 2-methyl-6-methoxy-l,2,3,4-tetrahydro-beta-carboline, 2-methy1-6-methoxy-l ,2,3,4-tetrahydro-beta-carboline and 2,9-dimethy1-1,2,3,4-tetrahydro-beta-carboline. The concentration and the type of these alkaloids are genetically fixed, but they can be intensely modulated by environmental variables such as shading, source and rate of available nitrogen in the soil, moisture stress, frosting, growing temperature. Moreover, they differ in the different parts of the plant and according to the growing stage. An equivalent group of alkaloids was also found in Arundo donax. Furthermore, the results of our preliminary biochemical researches on cultivated samples of P. canariensis, P. coemlescens, P. paradoxa and P. truncata are reported: ali these species contain indole alkaloids, probably indolalkylamines. Key words: Phalaris, Arundo, Psychoactive alkaloids.