A new dimeric alkaloid 1 has been isolated from Schizanthus grahamii and its structure determined by spectroscopic methods. Grahamine, an unusual tropane alkaloid containing a cyclobutane tricarboxylic acid as a central partial structure, was recently isolated from Schizanthus grahamii Gill (Salpiglossidae) and identified (1). This and other earlier chemical studies of the Schizanthus (2-5) have shown that this genus accumulates a number of tropane-derived alkaloids and may, therefore, be considered a typical member of the Solanaceae. We are here reporting the structure determination of schizanthine X [1], a new tropanol mesaconic acid di-ester, similar to other 3α,β-di-ester tropane derivatives previously isolated from S. grahamii (5).