Seven geranylated furocoumarins were isolated from the fruits of TETRADIUM DANIELLII (Benn.) T.G. Hartley (Rutaceae) and tested for their antimycobacterial activity against MYCOBACTERIUM FORTUITUM, M. SMEGMATIS and M. PHLEI. They were shown to be highly active, with minimal inhibitory concentrations (MICs) ranging from 8 to 64 microg/mL. Xanthotoxin and xanthotoxol, representing furocoumarins lacking the lipophilic geranyl side chain, were tested similarly and were shown to be inactive. Geraniol alone was inactive as well. The antimycobacterial activity of the substances was dependent on the position and polarity of the geranyl moiety. The compounds were purified using chromatographic methods. Structure elucidation was achieved with 1D and 2D NMR experiments.