The intestinal Protozoa found in a sample of 18,064 adults stationed on or affiliated with military stations in southern California but representing all States and many different segments of the population in the United States were, in order of increasing prevalence (% in parenthesis), the following: Embadomonas intestinalis (<0.1); Enteromonas hominis (<0.1); Dientamoeba fragilis (0.2); Trichomonas hominis (0.6); Iodamoeba bütschlii (1.7); Chilomastix mesnili (4.1); Entamoeba hartmanni (3.2); Entamoeba histolytica (2.9); Entamoeba coli (10.6); Giardia lamblia (11.5); Endolimax nana (13.2). Entamoeba polecki was found in one individual only. Host agegroups 24–34, 35–45, 46–56 showed no significant changes in prevalence for any species except Giardia lamblia, which decreased with increasing age.
San Bernardino County Health Department and Department of Biology, University of Southern California, Los Angeles. Present address 3956 Oakwood Place, Riverside, California.
Biometrical Laboratory, University of California Citrus Experiment Station, Riverside, California.