Production of alkaloids with both canthin-6-one and β-carboline structure by Ailanthus altissima cell cultures is reported. Besides canthin-6-one (1), 1-methoxycanthin-6-one (2), canthin-6-one-3-oxide (7), 1-methoxycanthin-6-one-3-oxide (8), 1-hydroxycanthin-6-one (3), 5-hydroxycanthin-6-one (6), β-carboline-1-propionic-acid (11), and 4-methoxy-β-carboline-1-carboxylic acid methylester (10), three new alkaloids are described. These are 2-hydroxycanthin-6-one (4), 4-hydroxycanthin-6-one (5), and 4,5-dihydrocanthin-6-one (9). Ailanthus altissima Swingle (Simaroubaceae) is known to be a producer of indole alkaloids and has been extensively studied (1-4). These alkaloids belong to the class of either the simple β-carboline or the more complex canthin-6-one derivatives. The literature has recently reported (5) cell cultures of A. altissima that produced canthin-6-one (1) and 1-methoxycanthin-6-one (2), which are the two most abundant alkaloids in the intact plant. We investigated the production of some minor alkaloids whose presence had been suspected during a previous study undertaken in order to clarify the different steps of their biosynthesis (6). Eleven alkaloids were identified and isolated in satisfactory yields from a batch of 50 liters of cell suspension cultures of A. altissima. Besides the main alkaloids 1 and 2, cell cultures produced their corresponding 3-oxides, 7 and 8, respectively, as well as β-carboline-1-propionic acid (11), 4-methoxy-β-carboline-1-carboxylic acid methylester (10), 5-hydroxycanthin-6-one (6) previously found in A. altissima (1,2,4), and 1-hydroxycanthin-6-one (3) found in Ailanthus giraldii (7). Furthermore, the following three alkaloids never before found in nature, 2-hydroxycanthin-6-one (4), 4-hydroxycanthin-6-one (5), and 4,5-dihydrocanthin-6-one (9), have been extracted. In spite of the predominant alkaloid canthin-6-one (1) produced in the amount of 300 μg/ml of cell suspension, each of the new compounds 4,5, and 9 represent 0.3% of the total alkaloids, and their production is 2 μg/ml or less.