During the Paraguayan War, Brazilian army and navy officers attributed outbreaks of combatant limb weakness with particular features such as tingling to palustrian causes. A dietary basis was not fully suspected at the time, and the popular name beriberi had not been coined. During wartime, there was a shortage in the food supply in addition to poor environmental conditions and diarrheal diseases, and many reports of "palustrian cachexia" were made. There are also reports of the use of native flora to feed troops, as well as alcoholism. There are also accounts of the death of horses with symptoms similar to those of combatants. It was reported that black soldiers were more resistant to "palustrian cachexia." This article presents the disease ecology and clinical manifestations of beriberi at wartime, linked to starvation and consumption of pickled food and native flora. These military explorations and operations in the Paraguayan War happened more than 150 y ago and present some aspects of wilderness medicine in the past.