The crystal structure of the 1:1 adduct hydrate of strychnine with 1,7-Cleve's acid (8-amino-2-naphthalenesulfonic acid), namely strychnine-8-ammonio-2-naphthalenesulfonate-water (1/1/3.5) has been determined and provides a unique example of a neutral association involving strychnine and an achiral zwitterionic acid species, previously unobserved in the structures of either strychnine or brucine addition compounds. Crystals are orthorhombic, space group P212121, with Z=4 in a cell with dimensions a=10.4484(8), b=30.850(3), c=9.4998(11) Ů Hydrogen bonding involving all available proton-donor and acceptor sites on all species gives rise to a three-dimensional framework polymer structure. The crystallographic literature for strychnine and brucine and their compounds is also reviewed.