In September, 1995 and January, 1996, six species offishes from Lake Cuitzeo, Michoacan, Mexico, were collected (Alloophorlls robllstus n=30, Goodea atripinnis n=30, Xenotoca variata n=41, Chirostoma jordani n=30, Caras"iu" aura tus n=30 and Oreochromis aureus n=30), to establish the infection levels reached by Posthodipla"tomum minimum, Clínostomum complanatum and Diplostomum (Tylodelphys) sp., in their hosts. Infection caused by P. minimum metacercariae was the most important helminthiasis consideling the number of hosts they parasite (five of six), and the high levels of abundance of the infection; we suggest that fish preferen ces and the generalist character of the trematode are the causes that determine this infection. Final1y, the role of goodeids and atherinids in transmission of infections in the lake is confirmed; the former being the main group mantainÍng such infections.In September, 1995 and January, 1996, six species offishes from Lake Cuitzeo, Michoacan, Mexico, were collected (Alloophorlls robllstus n=30, Goodea atripinnis n=30, Xenotoca variata n=41, Chirostoma jordani n=30, Caras"iu" aura tus n=30 and Oreochromis aureus n=30), to establish the infection levels reached by Posthodipla"tomum minimum, Clínostomum complanatum and Diplostomum (Tylodelphys) sp., in their hosts. Infection caused by P. minimum metacercariae was the most important helminthiasis consideling the number of hosts they parasite (five of six), and the high levels of abundance of the infection; we suggest that fish preferen ces and the generalist character of the trematode are the causes that determine this infection. Final1y, the role of goodeids and atherinids in transmission of infections in the lake is confirmed; the former being the main group mantainÍng such infections.