In order to study the variation of plasma fibronectin (FN) during malaria infection, two male monkeys (Macaca fascicularis) were splenectomized and infected with Plasmodium knowlesi. As parasitaemia increased FN concentration decreased gradually from 260 to 140 microgram/ml and 300 to 85 micrograms/ml for monkeys 1 and 2 respectively. The significance of this finding is discussed.