In the course of studies carried out in the 1930s on the alkaloidal constituents of Rauvolfia serpentina Benth. (Apocynaceae) roots collected from the Bihar province and Dehradun, Siddiqui (1-3) noted a marked difference in their character and yields due to climatic conditions. More recently, Siddiqui et al. studied roots from Thailand and Nepal, isolating sandwicoline (4), sandwicolidine (5) from Nepalian roots, and jmalicidine (6) from Thai roots. The present paper deals with the isolation and structure elucidation of another new base named rescinnamidine [1] (2', 3' -dihydrorescinnamine) from the roots of R. serpentina collected from Thailand. Rescinnamidine [1] has a molecular formula C36H48N2O9 (high resolution mass M+ 636.7420). Its uv spectrum showed maxima at 210, 225, 270, and 295 nm characteristic of methoxyindole alkaloids. The ir spectrum showed peaks at 3450 (N-H), 1725, and 1740 cm-1 (carbonyl stretchings), in addition to other peaks. The 1H and 13C nmr exhibited the presence of six methoxy groups while a fragment at m/z 397.2127 in the ms corresponding to C21H29N2O4 resulting from the loss of C12H15O5 indicated the presence of a trimethoxy-dihydrocinnamoyl ester in the molecule, supported by NMR signals including a two-proton singlet at δ 6.42 (H-5' and H-9'), a six-proton singlet at δ 3.84 (6'-OCH3 and 8'-OCH3), a three-proton singlet at δ 3.81 (7'-OCH3), and two two-proton triplets at δ 2.93 (J=7.5 Hz) and 2.63 (J=7.5 Hz) for H-2' and H-3'. The spectral data of [1] showed a close relation with the reserpine series of alkaloids and a one-proton doublet of double doublets at δ 4.78 led to the location of the dihydrocinnamoyl ester at C-18. The 1H- and 13C-nmr spectra further indicated a methoxy ester and two methoxy functions at C-11, C-16, and C-17, respectively. A broad singlet at δ 4.41 assigned to H-3 suggested its β-disposition. The structure of rescinnamidine [1] was finally substantiated by the 13C-nmr (broad band and spin echo) spectral data and by the hydrolysis of [1] into methyl reserpate. The stereochemistry of all the asymmetric centers of [1] is the same as reserpine and rescinnamine (8-11).