Four naphthoquinones were submitted to the action of diazomethane. The structure of the nine adducts, of which four were original, was determined. The protozoocidal activity of these compounds was evaluated in vitro against Plasmodium falciparum, Leishmania donovani, Trypanosoma brucei and Trichomonas vaginalis. The 2-methoxy-naphthoquinone <(3a)under bar> exhibited some activity and was more potent against these four protozoa than the reference drugs. The 2-methoxynaphthoquinone <(4a)under bar> showed more activity than chloroquine towards Plasmodium falciparum.