The structures of the two dimeric indole alkaloids 2 and 3 derived from aristone (1) have been determined from ¹H NMR, ¹³C NMR, and mass spectrometric data. A biogenetic hypothesis is proposed to account for the formation of a C-N bond between the two halves of the dimers, and a partial synthesis of 3 based on this hypothesis has been carried out by a coupling process involving radicals generated by chemical or photochemical reactions.