There has been some question about the identity of the illness variously called "fever and ague" or "intermittent fever" which appeared among the Indians of the lower Columbia and Willamette Valleys in the early 1830's. After a review of available evidence, this paper concludes that the disease was malaria and attempts a reconstruction of the events surrounding its appearance. Identification of fever and ague as malaria facilitates the formation of certain hypotheses about the epidemic's interaction with particular aspects of the native Chinookan and Kalapuyan cultures.