Because conservation biologists have postulated that infectious diseases may have potentiated the endangerment of the Attwater's prairie chicken (Tympanuchus cupido attwateri), free-living prairie chickens were surveyed from all remaining populations for helminthic endoparasites and antibody against the etiological agents of nine infectious diseases. Samples from 4 of 27 adult males were positive for anti-Pasteurella multocida antibody. All other serologic tests were negative (n = 19). We identified Dispharynx nasuta, a parasite previously associated with disease in other grouse from North America, in one of three adult Attwater's prairie chickens examined. Evidence of Tmichostrongylus cramae was found for eight of nine suitable samples, which represents the first report of this parasite in prairie grouse. The mean intensity of T. cramae in Attwater's prairie chicken was 1,019.3 (Range = 3-1,906; n = 3). Further work is needed to determine whether P. multocida, T. cramae, or D. nasuta are detrimental to Attwater's prairie chicken populations. If so, conservation biologists could reduce the prevalence and incidence of these parasites and potentially gain more time to address the habitat conditions thought to be the ultimate cause of population declines