Saponin C, a beta-glucosidase-treated saponin isolated from ethanol-water extracts of a South African collection of Tribulus terrestris, was shown by one- and two-dimensional NMR spectroscopy to be ruscogenin 1-O-alpha-L-rhamnopyranosyl-(1-->2)-beta-D-6)-acetylglucopyranoside++ +. GC-MS analysis of the hydrolysed ethanol-water (4:1) extracts of T.terrestris specimens from two of four sites, revealed high levels of ruscogenin and potentially lithogenic diosgenin saponins. Specimens from two other sites contained non-lithogenic saponins derived predominantly from tigogenin, neotigogenin, gitogenin and neo-gitogenin.