The quaternary β-carbolinium alkaloid nostocarboline from the cyanobacterium Nostoc 78-12A and ten bis-cationic dimeric derivatives were evaluated against four protozoan parasites and low micromolar values against Trypanosoma brucei, submicromolar values against Leishmania donovani and low nanomolar values against Plasmodium falciparum K1 were determined. Selectivity against rat myoblasts (L6 cells) was found to be up to > 2500 fold.