A total of 100 American coots, Fulica americana Gmelin, 1789, were examined for metazoan parasites from the Chihuahua Desert, Middle Rio Grande Valley Texas, and from the Upper Rio Grande Valley, Colorado, U.S.A., between 1984 and 1986. There was no significant difference in helminth species richness or median abundance between the component communities from the 2 localities. Fifteen of the 25 helminth species collected were in common to both, and similarity was 65%. The same species in each of the 4 taxa, Notocotylus pacifera, Diorchis americana, Amidostomum fulicae, and Polymorphus spp., had the highest prevalence and abundance in both, and the same 5 species of acanthocephalans were also in common. Eight of the 9 species of ectoparasites were common, and similarity was 91%. In both host species, Pseudomenopon pilosum and Rallicola advenus were the most prevalent and abundant mallophagans, and Laemobothrian atrum was the least. The nasal mite Rallynyssus caudistigmus was present in hosts from both localities. Of the 3 unidentified species of feather mites, species 1 was the most prevalent and abundant in Texas and absent in hosts from Colorado, and species 3 was the most prevalent in hosts from Colorado. The following helminth species were present in all 3 seasonal samples in Texas: A. fulicae, D. americana, Diorchis ransomi, N. pacifera, Polymorphus trochus, and Tetrameres globosa, whereas D. americana had the highest mean intensity in all 3. Overall, 70 species of helminths (33 trematodes, 15 cestodes, 14 nematodes, and 8 acanthocephalans) have been recorded in F. americana from North America. All species, except Echinostoma americanum, have been reported from other species of hosts. The majority of species are generalists (90%), although the following are specialists and largely predictable in American coots: trematodes (N. pacifera and Cyclocoelum mutabile); cestodes (D. americana, and D. ransomi); nematodes (A. fulicae, in adult coots only); Pelecitus fulicaeatrae; and the acanthocephalan, P. trochus.