A variety of naphthoquinones have veen prepared and evaluated in vitro against the causative agent of the cattle disease East Coast Fever-Theileria parva infection. It is concluded from structure-activity studies that a 2-hydroxyl moiety es essential for high activity. The most active compounds tested were 2-hydroxy-3-alkyl-1,4-naphthoquinones in which the alkyl moiety was cyclohexyl, cyclohexylcyclohexyl, tridecyl, or tetradecyl.