Higher plants represent a rich source of new molecules with pharmacological properties, which could become lead compounds for the development of new drug products. During the last decades, the renewed interest in investigating natural substances has led to the introduction of several important drugs, such as the anticancer substances vinblastine, vincristine, taxol and camptothecine derivatives, or the antimalarial agent artemisinin. Despite recent scientific and technological advances, parasitic diseases continue to affect millions of people in both tropical and subtropical zones of the world. On the other hand the drugs used for the treatment of most parasitic diseases are extremely limited. In this field, natural products constitute a reservoir of new molecules with potential therapeutic interest. An outline is presented here of some important results obtained by the Laboratory of Pharmacognosy and Phytochemistry of the University of Geneva on plants used to treat some of the neglected diseases. The strategy employed for the study of these plants is outlined, covering all aspects from the selection of plant material to the isolation of the active substances. Different bioactivities have been investigated such as the search for new molluscicidal and larvicidal agents. Results are also included for antileishimanial and antimalarial compounds.