The alkaloid composition of Hyoscyam us boveanus, H. desertorum, H. muticus and H. albus was investigated by capillary GLC and GLC-mass spectrometry. Altogether 39 alkaloids of the tropane and pyrrolidine types were identified. Several alkaloids were found in the different species for the first time, e.g., 22 alkaloids in H. boveanus, 13 in H. desertorum, 24 in H. muticus and 4 in H. albus. 3β-Hyoscyamine, dehydrohyoscyamine, phyllalbine, 3α-phenylacetyltropane, phenylacetylscopine as well as phygrine and 2,3-diacetonyl-N-methyl-pyrrolidine are apparently new for the genus Hyoscyamus. Alkaloid profiles and alkaloid contents of flowers, fruits, leaves, stems and roots were determined and their chemoecological functions discussed.