The bis-indoline alkaloid callichiline and five of its derivatives were investigated by the 13C NMR spectral method and their C shifts assigned. This analysis and biogenetic considerations limited the alkaloid to two structures of which one was shown by a single-crystal X-ray crystallographic analysis of the natural base to be the actual structure of the alkaloid. Callichiline crystallizes in the monoclinic system, space group P21, with a = 8.776(3) Å, b = 15.443(5) Å, c = 14.145(5) Å, β = 90.87(3)°, and Z = 2. Atomic positional and thermal parameters were refined by least-squares calculations to R = 0.052 over 2625 reflections measured by diffractometer. © 1983.