Since May 1993, 26 people have died of a "unique, previously unknown" viral illness that presents with flu-like symptoms and progresses rapidly to respiratory failure and death. Originally isolated in the four-corners region of the Southwest, the hantavirus responsible has now been isolated from patients in several other areas. In this article, we describe our experience with "the most puzzling case so far," an infection by a "cousin" of the Southwest hantaviral strain in a Louisiana bridgeworker. This case is unique not only because of the slightly different makeup of the virus, but also because of the absence of deer mice, the suspected carrier of the hantavirus, in the Louisiana region.