The protoberberine alkaloids berberine (1), palmatine (2), jatrorrhizine (3), and several berberine derivatives (4-10) were tested for antimalarial activity in vitro against Plasmodium falciparum and in vivo against Plasmodium berghei. The berberine derivatives 4-10 were designed and synthesized to maximize structural diversity within a modest set of compounds. Palmatine (2) and jatrorrhizine (3) were isolated as their chlorides from Enantia chlorantha. None of the protoberberine alkaloids was active in vivo, although compounds 1, 2, 3, 5, and 6 exhibited a potency comparable to that of quinine in vitro.